<?xml version="1.0" encoding="UTF-8"?>

<!--XBRL Document Created with the Workiva Platform-->
<!--Copyright 2026 Workiva-->
<!--r:019cb481-9caf-77c4-9ac8-9adfb0c3d7f0,g:ba84772a-3216-4426-bc24-eaa4a849c8e1-->
<link:linkbase xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xsi:schemaLocation="http://www.xbrl.org/2003/linkbase http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd">
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/all" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#all"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#hypercube-dimension"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-default"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#dimension-domain"/>
  <link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
  <link:roleRef roleURI="http://www.pacira.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="simple" xlink:href="pcrx-20260331.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFOPERATIONS" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019cb481-9e6f-722a-9d4f-ecfa977a5e0b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019cb481-9e6f-7c70-98ec-4db6a5153ace" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019cb481-9e6f-722a-9d4f-ecfa977a5e0b" xlink:to="loc_us-gaap_StatementTable_019cb481-9e6f-7c70-98ec-4db6a5153ace" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019cb481-9e6f-71fd-bcc4-f205c8017d17" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019cb481-9e6f-7c70-98ec-4db6a5153ace" xlink:to="loc_srt_ProductOrServiceAxis_019cb481-9e6f-71fd-bcc4-f205c8017d17" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019cb481-9e6f-71fd-bcc4-f205c8017d17_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019cb481-9e6f-71fd-bcc4-f205c8017d17" xlink:to="loc_srt_ProductsAndServicesDomain_019cb481-9e6f-71fd-bcc4-f205c8017d17_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019cb481-9e6f-7d93-b537-b685e5193518" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019cb481-9e6f-71fd-bcc4-f205c8017d17" xlink:to="loc_srt_ProductsAndServicesDomain_019cb481-9e6f-7d93-b537-b685e5193518" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_019cb481-9e6f-7d56-84e7-32e64da73822" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019cb481-9e6f-7d93-b537-b685e5193518" xlink:to="loc_us-gaap_ProductMember_019cb481-9e6f-7d56-84e7-32e64da73822" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RoyaltyMember_019cb481-9e6f-70ee-911c-8b4f5fcb0a40" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RoyaltyMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019cb481-9e6f-7d93-b537-b685e5193518" xlink:to="loc_us-gaap_RoyaltyMember_019cb481-9e6f-70ee-911c-8b4f5fcb0a40" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenuesAbstract_019cb481-9e6f-7829-a9de-71bb3cfb9553" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenuesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cb481-9e6f-722a-9d4f-ecfa977a5e0b" xlink:to="loc_us-gaap_RevenuesAbstract_019cb481-9e6f-7829-a9de-71bb3cfb9553" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019cb481-9e6f-7181-a2c7-3deaa83bc445" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_RevenuesAbstract_019cb481-9e6f-7829-a9de-71bb3cfb9553" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019cb481-9e6f-7181-a2c7-3deaa83bc445" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingExpensesAbstract_019cb481-9e6f-7c82-91e4-8c01b6af2880" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingExpensesAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cb481-9e6f-722a-9d4f-ecfa977a5e0b" xlink:to="loc_us-gaap_OperatingExpensesAbstract_019cb481-9e6f-7c82-91e4-8c01b6af2880" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfRevenue_019cb481-9e6f-7c3b-b857-1fd32ada26c3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019cb481-9e6f-7c82-91e4-8c01b6af2880" xlink:to="loc_us-gaap_CostOfRevenue_019cb481-9e6f-7c3b-b857-1fd32ada26c3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpense_019cb481-9e6f-7d4a-bf15-cc4d05be4eff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019cb481-9e6f-7c82-91e4-8c01b6af2880" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpense_019cb481-9e6f-7d4a-bf15-cc4d05be4eff" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019cb481-9e6f-7093-91e8-9bab163beb2a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019cb481-9e6f-7c82-91e4-8c01b6af2880" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpense_019cb481-9e6f-7093-91e8-9bab163beb2a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_019cb481-9e6f-79c1-95ce-8df81920c0ca" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019cb481-9e6f-7c82-91e4-8c01b6af2880" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_019cb481-9e6f-79c1-95ce-8df81920c0ca" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherOperatingIncomeExpenseNet_019d771f-a062-7cce-b425-8068760e1293" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherOperatingIncomeExpenseNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019cb481-9e6f-7c82-91e4-8c01b6af2880" xlink:to="loc_us-gaap_OtherOperatingIncomeExpenseNet_019d771f-a062-7cce-b425-8068760e1293" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_019cb481-9e6f-730d-811d-194bbf89c5e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_OperatingExpensesAbstract_019cb481-9e6f-7c82-91e4-8c01b6af2880" xlink:to="loc_us-gaap_CostsAndExpenses_019cb481-9e6f-730d-811d-194bbf89c5e1" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OperatingIncomeLoss_019cb481-9e6f-7dff-8878-d1904a685417" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OperatingIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cb481-9e6f-722a-9d4f-ecfa977a5e0b" xlink:to="loc_us-gaap_OperatingIncomeLoss_019cb481-9e6f-7dff-8878-d1904a685417" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019cb481-9e6f-7420-b956-d1f4dea9921f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonoperatingIncomeExpenseAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cb481-9e6f-722a-9d4f-ecfa977a5e0b" xlink:to="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019cb481-9e6f-7420-b956-d1f4dea9921f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InvestmentIncomeInterest_019cb481-9e6f-7bb3-a583-ec91aa90b386" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InvestmentIncomeInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019cb481-9e6f-7420-b956-d1f4dea9921f" xlink:to="loc_us-gaap_InvestmentIncomeInterest_019cb481-9e6f-7bb3-a583-ec91aa90b386" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestExpenseNonoperating_019cb481-9e6f-7a25-9168-cca44d23e0e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestExpenseNonoperating"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019cb481-9e6f-7420-b956-d1f4dea9921f" xlink:to="loc_us-gaap_InterestExpenseNonoperating_019cb481-9e6f-7a25-9168-cca44d23e0e9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherNonoperatingIncomeExpense_019cb481-9e6f-72e1-bc21-e6124fc0cc54" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherNonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019cb481-9e6f-7420-b956-d1f4dea9921f" xlink:to="loc_us-gaap_OtherNonoperatingIncomeExpense_019cb481-9e6f-72e1-bc21-e6124fc0cc54" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019cb481-9e6f-7a70-8a03-d70618108f5d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NonoperatingIncomeExpenseAbstract_019cb481-9e6f-7420-b956-d1f4dea9921f" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019cb481-9e6f-7a70-8a03-d70618108f5d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019cb481-9e6f-7613-98bd-586da1182ff7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cb481-9e6f-722a-9d4f-ecfa977a5e0b" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019cb481-9e6f-7613-98bd-586da1182ff7" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019cb481-9e6f-7c45-ad12-335e23e6986b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cb481-9e6f-722a-9d4f-ecfa977a5e0b" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019cb481-9e6f-7c45-ad12-335e23e6986b" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019cb481-9e6f-7528-a1da-6a2329262cec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cb481-9e6f-722a-9d4f-ecfa977a5e0b" xlink:to="loc_us-gaap_NetIncomeLoss_019cb481-9e6f-7528-a1da-6a2329262cec" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareAbstract_019cb481-9e6f-7645-bd07-6d65d9341cd7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cb481-9e6f-722a-9d4f-ecfa977a5e0b" xlink:to="loc_us-gaap_EarningsPerShareAbstract_019cb481-9e6f-7645-bd07-6d65d9341cd7" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_019cb481-9e6f-7b0f-ab71-48fb03154673" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_019cb481-9e6f-7645-bd07-6d65d9341cd7" xlink:to="loc_us-gaap_EarningsPerShareBasic_019cb481-9e6f-7b0f-ab71-48fb03154673" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_019cb481-9e6f-73d0-b393-6fa30c794487" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EarningsPerShareAbstract_019cb481-9e6f-7645-bd07-6d65d9341cd7" xlink:to="loc_us-gaap_EarningsPerShareDiluted_019cb481-9e6f-73d0-b393-6fa30c794487" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019cb481-9e6f-78f6-9efa-350aea47730b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cb481-9e6f-722a-9d4f-ecfa977a5e0b" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019cb481-9e6f-78f6-9efa-350aea47730b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019cb481-9e6f-7d44-bee5-33585ba514a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019cb481-9e6f-78f6-9efa-350aea47730b" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019cb481-9e6f-7d44-bee5-33585ba514a8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019cb481-9e6f-7cfe-9768-a79698f6034b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019cb481-9e6f-78f6-9efa-350aea47730b" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019cb481-9e6f-7cfe-9768-a79698f6034b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="simple" xlink:href="pcrx-20260331.xsd#CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/CONDENSEDCONSOLIDATEDSTATEMENTSOFSTOCKHOLDERSEQUITY" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementLineItems_019cb481-9e6f-71a7-9b08-f370c655a8ff" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementTable_019cb481-9e6f-7f69-98d7-86ddf1820079" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_StatementLineItems_019cb481-9e6f-71a7-9b08-f370c655a8ff" xlink:to="loc_us-gaap_StatementTable_019cb481-9e6f-7f69-98d7-86ddf1820079" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019cb481-9e6f-7837-8dc4-2c2f532b75f4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_StatementTable_019cb481-9e6f-7f69-98d7-86ddf1820079" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019cb481-9e6f-7837-8dc4-2c2f532b75f4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019cb481-9e6f-7837-8dc4-2c2f532b75f4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019cb481-9e6f-7837-8dc4-2c2f532b75f4" xlink:to="loc_us-gaap_EquityComponentDomain_019cb481-9e6f-7837-8dc4-2c2f532b75f4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019cb481-9e6f-7137-ba18-114d88d80ae9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019cb481-9e6f-7837-8dc4-2c2f532b75f4" xlink:to="loc_us-gaap_EquityComponentDomain_019cb481-9e6f-7137-ba18-114d88d80ae9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockMember_019cb481-9e6f-7878-ae53-1fc213358b5a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019cb481-9e6f-7137-ba18-114d88d80ae9" xlink:to="loc_us-gaap_CommonStockMember_019cb481-9e6f-7878-ae53-1fc213358b5a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonMember_019cb481-9e6f-748e-9ea1-6c48cbd6b2c8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019cb481-9e6f-7137-ba18-114d88d80ae9" xlink:to="loc_us-gaap_TreasuryStockCommonMember_019cb481-9e6f-748e-9ea1-6c48cbd6b2c8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019cb481-9e6f-71be-b60e-91c0b6794548" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019cb481-9e6f-7137-ba18-114d88d80ae9" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019cb481-9e6f-71be-b60e-91c0b6794548" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RetainedEarningsMember_019cb481-9e6f-72bb-99a6-89e5ee68c455" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RetainedEarningsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019cb481-9e6f-7137-ba18-114d88d80ae9" xlink:to="loc_us-gaap_RetainedEarningsMember_019cb481-9e6f-72bb-99a6-89e5ee68c455" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019cb481-9e6f-73b8-a771-4dbcf23664c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019cb481-9e6f-7137-ba18-114d88d80ae9" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019cb481-9e6f-73b8-a771-4dbcf23664c2" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncreaseDecreaseInStockholdersEquityRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_StatementLineItems_019cb481-9e6f-71a7-9b08-f370c655a8ff" xlink:to="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019cb481-9e6f-720f-ba3a-f993decff7e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:to="loc_us-gaap_CommonStockSharesOutstanding_019cb481-9e6f-720f-ba3a-f993decff7e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019cb481-9e6f-7156-807e-11a6a44f32d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:to="loc_us-gaap_TreasuryStockCommonShares_019cb481-9e6f-7156-807e-11a6a44f32d3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019cb481-9e6f-7f43-8f93-5c3ac0ef054c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:to="loc_us-gaap_StockholdersEquity_019cb481-9e6f-7f43-8f93-5c3ac0ef054c" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019dbace-38b9-7f48-9de0-f831ec729c78" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019dbace-38b9-7f48-9de0-f831ec729c78" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019dbace-38b9-7805-b42d-251282fa45a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueStockOptionsExercised_019dbace-38b9-7805-b42d-251282fa45a3" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019cb481-9e6f-7729-98a9-79ef5098f59e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesRestrictedStockAwardNetOfForfeitures_019cb481-9e6f-7729-98a9-79ef5098f59e" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_019cb481-9e6f-7c90-86a9-4696e0dcd80a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:to="loc_us-gaap_StockIssuedDuringPeriodValueRestrictedStockAwardNetOfForfeitures_019cb481-9e6f-7c90-86a9-4696e0dcd80a" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_019cb481-9e6f-798f-97ab-162522683d8e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:to="loc_us-gaap_SharesPaidForTaxWithholdingForShareBasedCompensation_019cb481-9e6f-798f-97ab-162522683d8e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_019cb481-9e6f-78ac-a930-332db7958a69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:to="loc_us-gaap_AdjustmentsRelatedToTaxWithholdingForShareBasedCompensation_019cb481-9e6f-78ac-a930-332db7958a69" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019cb481-9e6f-78c2-ac46-68c0797c50d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:to="loc_us-gaap_AdjustmentsToAdditionalPaidInCapitalSharebasedCompensationRequisiteServicePeriodRecognitionValue_019cb481-9e6f-78c2-ac46-68c0797c50d4" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockSharesAcquired_019cb481-9e6f-7a21-8c1a-7c531f2f2394" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockSharesAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:to="loc_us-gaap_TreasuryStockSharesAcquired_019cb481-9e6f-7a21-8c1a-7c531f2f2394" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_019cb481-9e6f-74db-981a-f0e4cd40d02e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockValueAcquiredCostMethod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:to="loc_us-gaap_TreasuryStockValueAcquiredCostMethod_019cb481-9e6f-74db-981a-f0e4cd40d02e" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019cb481-9e6f-7970-9229-9b7b5dd3a4e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent_019cb481-9e6f-7970-9229-9b7b5dd3a4e3" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019cb481-9e6f-7dfd-a572-bd5c52efbfdb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncreaseDecreaseInStockholdersEquityRollForward_019cb481-9e6f-7a42-b195-e6ef0469dd2e" xlink:to="loc_us-gaap_NetIncomeLoss_019cb481-9e6f-7dfd-a572-bd5c52efbfdb" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommonStockSharesOutstanding_019cb481-9e6f-7bdf-91e2-f4c49ef3d0d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommonStockSharesOutstanding"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TreasuryStockCommonShares_019cb481-9e6f-7af1-84ff-f12d9e94faf4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TreasuryStockCommonShares"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019cb481-9e6f-7824-b9e8-2e16a31b00d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/DESCRIPTIONOFBUSINESSDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#DESCRIPTIONOFBUSINESSDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/DESCRIPTIONOFBUSINESSDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9e6f-7084-806f-22aa8d866e47" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_019cb481-9e6f-7bf0-98d3-a1a2f0823a79" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9e6f-7084-806f-22aa8d866e47" xlink:to="loc_us-gaap_ConcentrationRiskTable_019cb481-9e6f-7bf0-98d3-a1a2f0823a79" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019cb481-9e6f-7dd2-9090-0821ab8a8957" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019cb481-9e6f-7bf0-98d3-a1a2f0823a79" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019cb481-9e6f-7dd2-9090-0821ab8a8957" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cb481-9e6f-7dd2-9090-0821ab8a8957_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019cb481-9e6f-7dd2-9090-0821ab8a8957" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cb481-9e6f-7dd2-9090-0821ab8a8957_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cb481-9e6f-7430-b1fd-b3ce39c82ad4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019cb481-9e6f-7dd2-9090-0821ab8a8957" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cb481-9e6f-7430-b1fd-b3ce39c82ad4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_GQBioTherapeuticsGmbHMember_019cb481-9e6f-73d7-895a-933b08529928" xlink:href="pcrx-20260331.xsd#pcrx_GQBioTherapeuticsGmbHMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cb481-9e6f-7430-b1fd-b3ce39c82ad4" xlink:to="loc_pcrx_GQBioTherapeuticsGmbHMember_019cb481-9e6f-73d7-895a-933b08529928" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019cb481-9e6f-7fa8-86b8-4ef905d36241" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019cb481-9e6f-7bf0-98d3-a1a2f0823a79" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019cb481-9e6f-7fa8-86b8-4ef905d36241" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019cb481-9e6f-7fa8-86b8-4ef905d36241_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019cb481-9e6f-7fa8-86b8-4ef905d36241" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019cb481-9e6f-7fa8-86b8-4ef905d36241_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019cb481-9e6f-7ff9-8b13-e46ce6a46ef2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019cb481-9e6f-7fa8-86b8-4ef905d36241" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019cb481-9e6f-7ff9-8b13-e46ce6a46ef2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_019cb481-9e6f-7c96-a11e-29a5205dbd01" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019cb481-9e6f-7ff9-8b13-e46ce6a46ef2" xlink:to="loc_us-gaap_SalesRevenueNetMember_019cb481-9e6f-7c96-a11e-29a5205dbd01" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019cb481-9e6f-78c6-941c-b93fe178e589" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019cb481-9e6f-7bf0-98d3-a1a2f0823a79" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019cb481-9e6f-78c6-941c-b93fe178e589" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019cb481-9e6f-78c6-941c-b93fe178e589_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019cb481-9e6f-78c6-941c-b93fe178e589" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019cb481-9e6f-78c6-941c-b93fe178e589_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019cb481-9e6f-788b-87f1-337290502f47" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019cb481-9e6f-78c6-941c-b93fe178e589" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019cb481-9e6f-788b-87f1-337290502f47" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductConcentrationRiskMember_019cb481-9e6f-7852-b8f9-a1a1fd4035ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019cb481-9e6f-788b-87f1-337290502f47" xlink:to="loc_us-gaap_ProductConcentrationRiskMember_019cb481-9e6f-7852-b8f9-a1a1fd4035ec" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019cb481-9e6f-73c2-becc-280893f0617d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9e6f-7084-806f-22aa8d866e47" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019cb481-9e6f-73c2-becc-280893f0617d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ConcentrationRiskNumberOfProducts_019cb481-9e6f-7129-a100-fc581fa52743" xlink:href="pcrx-20260331.xsd#pcrx_ConcentrationRiskNumberOfProducts"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9e6f-7084-806f-22aa8d866e47" xlink:to="loc_pcrx_ConcentrationRiskNumberOfProducts_019cb481-9e6f-7129-a100-fc581fa52743" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_019dbdae-4194-755d-8ab7-ea736c125393" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_019dbdae-4194-7101-9702-a941750c72d9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019dbdae-4194-755d-8ab7-ea736c125393" xlink:to="loc_us-gaap_ConcentrationRiskTable_019dbdae-4194-7101-9702-a941750c72d9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019dbdae-4194-7c73-977c-908d3b88e2f1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019dbdae-4194-7101-9702-a941750c72d9" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019dbdae-4194-7c73-977c-908d3b88e2f1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019dbdae-4194-7c73-977c-908d3b88e2f1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019dbdae-4194-7c73-977c-908d3b88e2f1" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019dbdae-4194-7c73-977c-908d3b88e2f1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019dbdae-4194-7e18-bed8-1ad757b44dac" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019dbdae-4194-7c73-977c-908d3b88e2f1" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019dbdae-4194-7e18-bed8-1ad757b44dac" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_019dbdae-4194-71cd-8389-f9636231a19d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019dbdae-4194-7e18-bed8-1ad757b44dac" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_019dbdae-4194-71cd-8389-f9636231a19d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ConcentrationRiskNumberOfCustomers_019dbdae-4194-78c4-96a3-1f8af339c810" xlink:href="pcrx-20260331.xsd#pcrx_ConcentrationRiskNumberOfCustomers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019dbdae-4194-755d-8ab7-ea736c125393" xlink:to="loc_pcrx_ConcentrationRiskNumberOfCustomers_019dbdae-4194-78c4-96a3-1f8af339c810" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofPercentageofRevenueComprisedofThreeLargestCustomersDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofPercentageofRevenueComprisedofThreeLargestCustomersDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/SUMMARYOFSIGNIFICANTACCOUNTINGPOLICIESScheduleofPercentageofRevenueComprisedofThreeLargestCustomersDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9e6f-743d-9501-cc57f6e956b9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_019cb481-9e6f-7751-8a5c-ebd84e9a9b1c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9e6f-743d-9501-cc57f6e956b9" xlink:to="loc_us-gaap_ConcentrationRiskTable_019cb481-9e6f-7751-8a5c-ebd84e9a9b1c" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019cb481-9e6f-7718-aed2-c26c555a1380" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019cb481-9e6f-7751-8a5c-ebd84e9a9b1c" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019cb481-9e6f-7718-aed2-c26c555a1380" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019cb481-9e6f-7718-aed2-c26c555a1380_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019cb481-9e6f-7718-aed2-c26c555a1380" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019cb481-9e6f-7718-aed2-c26c555a1380_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019cb481-9e6f-70f8-a14b-9125ed3e4125" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019cb481-9e6f-7718-aed2-c26c555a1380" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019cb481-9e6f-70f8-a14b-9125ed3e4125" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_019cb481-9e6f-78e8-ae82-025f3240de5c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019cb481-9e6f-70f8-a14b-9125ed3e4125" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_019cb481-9e6f-78e8-ae82-025f3240de5c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019cb481-9e6f-77c1-91b4-c5f14fbbac37" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019cb481-9e6f-7751-8a5c-ebd84e9a9b1c" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019cb481-9e6f-77c1-91b4-c5f14fbbac37" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019cb481-9e6f-77c1-91b4-c5f14fbbac37_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019cb481-9e6f-77c1-91b4-c5f14fbbac37" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019cb481-9e6f-77c1-91b4-c5f14fbbac37_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019cb481-9e6f-79f1-b283-aa018b0e5c55" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019cb481-9e6f-77c1-91b4-c5f14fbbac37" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019cb481-9e6f-79f1-b283-aa018b0e5c55" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SalesRevenueNetMember_019cb481-9e6f-7afb-901d-c7c2dbcda4ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SalesRevenueNetMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019cb481-9e6f-79f1-b283-aa018b0e5c55" xlink:to="loc_us-gaap_SalesRevenueNetMember_019cb481-9e6f-7afb-901d-c7c2dbcda4ae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019cb481-9e6f-739f-9030-81da0d1d875e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019cb481-9e6f-7751-8a5c-ebd84e9a9b1c" xlink:to="loc_srt_MajorCustomersAxis_019cb481-9e6f-739f-9030-81da0d1d875e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019cb481-9e6f-739f-9030-81da0d1d875e_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019cb481-9e6f-739f-9030-81da0d1d875e" xlink:to="loc_srt_NameOfMajorCustomerDomain_019cb481-9e6f-739f-9030-81da0d1d875e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019cb481-9e6f-7e57-99c0-122ee34c5f1c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019cb481-9e6f-739f-9030-81da0d1d875e" xlink:to="loc_srt_NameOfMajorCustomerDomain_019cb481-9e6f-7e57-99c0-122ee34c5f1c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_LargestCustomerMember_019cb481-9e6f-7a88-9693-c408c53b399d" xlink:href="pcrx-20260331.xsd#pcrx_LargestCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019cb481-9e6f-7e57-99c0-122ee34c5f1c" xlink:to="loc_pcrx_LargestCustomerMember_019cb481-9e6f-7a88-9693-c408c53b399d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_SecondLargestCustomerMember_019cb481-9e6f-7131-944e-f58168091b5c" xlink:href="pcrx-20260331.xsd#pcrx_SecondLargestCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019cb481-9e6f-7e57-99c0-122ee34c5f1c" xlink:to="loc_pcrx_SecondLargestCustomerMember_019cb481-9e6f-7131-944e-f58168091b5c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ThirdLargestCustomerMember_019cb481-9e6f-7acb-afc9-5ffbbd570300" xlink:href="pcrx-20260331.xsd#pcrx_ThirdLargestCustomerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019cb481-9e6f-7e57-99c0-122ee34c5f1c" xlink:to="loc_pcrx_ThirdLargestCustomerMember_019cb481-9e6f-7acb-afc9-5ffbbd570300" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ThreeLargestCustomersMember_019cb481-9e6f-78ba-82c9-8a9d25564443" xlink:href="pcrx-20260331.xsd#pcrx_ThreeLargestCustomersMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019cb481-9e6f-7e57-99c0-122ee34c5f1c" xlink:to="loc_pcrx_ThreeLargestCustomersMember_019cb481-9e6f-78ba-82c9-8a9d25564443" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ConcentrationRiskNumberOfCustomers_019cb481-9e6f-7d7c-b78e-a7c7373e18b8" xlink:href="pcrx-20260331.xsd#pcrx_ConcentrationRiskNumberOfCustomers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9e6f-743d-9501-cc57f6e956b9" xlink:to="loc_pcrx_ConcentrationRiskNumberOfCustomers_019cb481-9e6f-7d7c-b78e-a7c7373e18b8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019cb481-9e6f-7222-866d-06b3bd00d837" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9e6f-743d-9501-cc57f6e956b9" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019cb481-9e6f-7222-866d-06b3bd00d837" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/REVENUENarrativeDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#REVENUENarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/REVENUENarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019cb481-9e6f-7765-a560-3c2d6fd45230" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019cb481-9e6f-7f69-802c-456392891fba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019cb481-9e6f-7765-a560-3c2d6fd45230" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019cb481-9e6f-7f69-802c-456392891fba" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019cb481-9e6f-7216-9763-7a08557a0ce2" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019cb481-9e6f-7f69-802c-456392891fba" xlink:to="loc_srt_RangeAxis_019cb481-9e6f-7216-9763-7a08557a0ce2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019cb481-9e6f-7216-9763-7a08557a0ce2_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019cb481-9e6f-7216-9763-7a08557a0ce2" xlink:to="loc_srt_RangeMember_019cb481-9e6f-7216-9763-7a08557a0ce2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019cb481-9e6f-790f-a5f1-d8649bbb4cb2" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019cb481-9e6f-7216-9763-7a08557a0ce2" xlink:to="loc_srt_RangeMember_019cb481-9e6f-790f-a5f1-d8649bbb4cb2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019cb481-9e6f-7fe4-aed6-f79ddfc8eedb" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019cb481-9e6f-790f-a5f1-d8649bbb4cb2" xlink:to="loc_srt_MinimumMember_019cb481-9e6f-7fe4-aed6-f79ddfc8eedb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019cb481-9e6f-7d2d-a35e-5919de590cd5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019cb481-9e6f-790f-a5f1-d8649bbb4cb2" xlink:to="loc_srt_MaximumMember_019cb481-9e6f-7d2d-a35e-5919de590cd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_AccountsReceivablePaymentTerms_019cb481-9e6f-7363-8cdf-4b6866868552" xlink:href="pcrx-20260331.xsd#pcrx_AccountsReceivablePaymentTerms"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019cb481-9e6f-7765-a560-3c2d6fd45230" xlink:to="loc_pcrx_AccountsReceivablePaymentTerms_019cb481-9e6f-7363-8cdf-4b6866868552" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/REVENUEScheduleofDisaggregatedRevenueDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#REVENUEScheduleofDisaggregatedRevenueDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/REVENUEScheduleofDisaggregatedRevenueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueLineItems_019cb481-9e6f-7f36-9d40-ab19e8d42ceb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DisaggregationOfRevenueTable_019cb481-9e6f-7802-bbbf-b45e19cb72b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DisaggregationOfRevenueTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019cb481-9e6f-7f36-9d40-ab19e8d42ceb" xlink:to="loc_us-gaap_DisaggregationOfRevenueTable_019cb481-9e6f-7802-bbbf-b45e19cb72b0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019cb481-9e6f-7a53-ae68-ef94ba7ec84c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DisaggregationOfRevenueTable_019cb481-9e6f-7802-bbbf-b45e19cb72b0" xlink:to="loc_srt_ProductOrServiceAxis_019cb481-9e6f-7a53-ae68-ef94ba7ec84c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019cb481-9e6f-7a53-ae68-ef94ba7ec84c_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019cb481-9e6f-7a53-ae68-ef94ba7ec84c" xlink:to="loc_srt_ProductsAndServicesDomain_019cb481-9e6f-7a53-ae68-ef94ba7ec84c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019cb481-9e6f-70c4-8245-806eecdf33be" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019cb481-9e6f-7a53-ae68-ef94ba7ec84c" xlink:to="loc_srt_ProductsAndServicesDomain_019cb481-9e6f-70c4-8245-806eecdf33be" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProductMember_019cb481-9e6f-7c37-9733-e3e9123a2970" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProductMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019cb481-9e6f-70c4-8245-806eecdf33be" xlink:to="loc_us-gaap_ProductMember_019cb481-9e6f-7c37-9733-e3e9123a2970" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_EXPARELMember_019cb481-9e6f-74fe-abe6-890b30937899" xlink:href="pcrx-20260331.xsd#pcrx_EXPARELMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_019cb481-9e6f-7c37-9733-e3e9123a2970" xlink:to="loc_pcrx_EXPARELMember_019cb481-9e6f-74fe-abe6-890b30937899" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ZILRETTAMember_019cb481-9e6f-7041-b502-ed822efe08e0" xlink:href="pcrx-20260331.xsd#pcrx_ZILRETTAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_019cb481-9e6f-7c37-9733-e3e9123a2970" xlink:to="loc_pcrx_ZILRETTAMember_019cb481-9e6f-7041-b502-ed822efe08e0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_IoveraMember_019cb481-9e6f-770f-8f05-f5d57d3859f6" xlink:href="pcrx-20260331.xsd#pcrx_IoveraMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_019cb481-9e6f-7c37-9733-e3e9123a2970" xlink:to="loc_pcrx_IoveraMember_019cb481-9e6f-770f-8f05-f5d57d3859f6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_BupivacaineLiposomeInjectableSuspensionMember_019cb481-9e6f-7cfc-9b57-9c4f24472894" xlink:href="pcrx-20260331.xsd#pcrx_BupivacaineLiposomeInjectableSuspensionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ProductMember_019cb481-9e6f-7c37-9733-e3e9123a2970" xlink:to="loc_pcrx_BupivacaineLiposomeInjectableSuspensionMember_019cb481-9e6f-7cfc-9b57-9c4f24472894" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019cb481-9e6f-7346-8018-2cb6fad002dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DisaggregationOfRevenueLineItems_019cb481-9e6f-7f36-9d40-ab19e8d42ceb" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019cb481-9e6f-7346-8018-2cb6fad002dc" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/FIXEDASSETSScheduleofFixedAssetsSummarizedbyMajorCategoryDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#FIXEDASSETSScheduleofFixedAssetsSummarizedbyMajorCategoryDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/FIXEDASSETSScheduleofFixedAssetsSummarizedbyMajorCategoryDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019cb481-9e6f-7994-8384-210de32a2deb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019cb481-9e6f-7180-bd9e-9940d26950cb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019cb481-9e6f-7994-8384-210de32a2deb" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019cb481-9e6f-7180-bd9e-9940d26950cb" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019cb481-9e6f-78b6-ad59-96f32bc35d3c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019cb481-9e6f-7180-bd9e-9940d26950cb" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019cb481-9e6f-78b6-ad59-96f32bc35d3c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cb481-9e6f-78b6-ad59-96f32bc35d3c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019cb481-9e6f-78b6-ad59-96f32bc35d3c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cb481-9e6f-78b6-ad59-96f32bc35d3c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cb481-9e6f-79b5-bf56-92fa4b8cb197" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019cb481-9e6f-78b6-ad59-96f32bc35d3c" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cb481-9e6f-79b5-bf56-92fa4b8cb197" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MachineryAndEquipmentMember_019cb481-9e6f-747a-8720-060927f9d080" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MachineryAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cb481-9e6f-79b5-bf56-92fa4b8cb197" xlink:to="loc_us-gaap_MachineryAndEquipmentMember_019cb481-9e6f-747a-8720-060927f9d080" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019cb481-9e6f-76e4-a9d8-b257613a80ee" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cb481-9e6f-79b5-bf56-92fa4b8cb197" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019cb481-9e6f-76e4-a9d8-b257613a80ee" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ComputerEquipmentAndSoftwareMember_019cb481-9e6f-7b6d-9863-4c421b209fde" xlink:href="pcrx-20260331.xsd#pcrx_ComputerEquipmentAndSoftwareMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cb481-9e6f-79b5-bf56-92fa4b8cb197" xlink:to="loc_pcrx_ComputerEquipmentAndSoftwareMember_019cb481-9e6f-7b6d-9863-4c421b209fde" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FurnitureAndFixturesMember_019cb481-9e6f-7b79-858e-091c2cf62b50" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FurnitureAndFixturesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cb481-9e6f-79b5-bf56-92fa4b8cb197" xlink:to="loc_us-gaap_FurnitureAndFixturesMember_019cb481-9e6f-7b79-858e-091c2cf62b50" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConstructionInProgressMember_019cb481-9e6f-767c-96f8-f6e386e8a1e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConstructionInProgressMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cb481-9e6f-79b5-bf56-92fa4b8cb197" xlink:to="loc_us-gaap_ConstructionInProgressMember_019cb481-9e6f-767c-96f8-f6e386e8a1e5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentGross_019cb481-9e6f-7606-818b-44e2220af7d0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019cb481-9e6f-7994-8384-210de32a2deb" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentGross_019cb481-9e6f-7606-818b-44e2220af7d0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019cb481-9e6f-7230-89cb-dba3e9b9a9e8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019cb481-9e6f-7994-8384-210de32a2deb" xlink:to="loc_us-gaap_AccumulatedDepreciationDepletionAndAmortizationPropertyPlantAndEquipment_019cb481-9e6f-7230-89cb-dba3e9b9a9e8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019cb481-9e6f-7919-98da-62554d521d1f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019cb481-9e6f-7994-8384-210de32a2deb" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019cb481-9e6f-7919-98da-62554d521d1f" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/FIXEDASSETSNarrativeDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#FIXEDASSETSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/FIXEDASSETSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019cb481-9e6f-7e60-a385-ba8663e2825d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019cb481-9e6f-7e6f-9988-e8744988da69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfPropertyPlantAndEquipmentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019cb481-9e6f-7e60-a385-ba8663e2825d" xlink:to="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019cb481-9e6f-7e6f-9988-e8744988da69" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019cb481-9e6f-7449-81bf-422c15f62dc5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019cb481-9e6f-7e6f-9988-e8744988da69" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019cb481-9e6f-7449-81bf-422c15f62dc5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cb481-9e6f-7449-81bf-422c15f62dc5_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019cb481-9e6f-7449-81bf-422c15f62dc5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cb481-9e6f-7449-81bf-422c15f62dc5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cb481-9e6f-792d-a2a4-34d98ebf57b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentByTypeAxis_019cb481-9e6f-7449-81bf-422c15f62dc5" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cb481-9e6f-792d-a2a4-34d98ebf57b0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LeaseholdImprovementsMember_019cb481-9e6f-7159-89cc-792e0217d0da" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LeaseholdImprovementsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentTypeDomain_019cb481-9e6f-792d-a2a4-34d98ebf57b0" xlink:to="loc_us-gaap_LeaseholdImprovementsMember_019cb481-9e6f-7159-89cc-792e0217d0da" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019cb481-9e6f-7245-999e-ed275c90f138" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfPropertyPlantAndEquipmentTable_019cb481-9e6f-7e6f-9988-e8744988da69" xlink:to="loc_srt_StatementGeographicalAxis_019cb481-9e6f-7245-999e-ed275c90f138" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019cb481-9e6f-7245-999e-ed275c90f138_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019cb481-9e6f-7245-999e-ed275c90f138" xlink:to="loc_srt_SegmentGeographicalDomain_019cb481-9e6f-7245-999e-ed275c90f138_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019cb481-9e6f-7518-b599-f092d2726b19" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019cb481-9e6f-7245-999e-ed275c90f138" xlink:to="loc_srt_SegmentGeographicalDomain_019cb481-9e6f-7518-b599-f092d2726b19" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonUsMember_019cb481-9e6f-717d-9901-a76a6c098510" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonUsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019cb481-9e6f-7518-b599-f092d2726b19" xlink:to="loc_us-gaap_NonUsMember_019cb481-9e6f-717d-9901-a76a6c098510" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Depreciation_019cb481-9e6f-7cb9-a607-787bf30cc91d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Depreciation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019cb481-9e6f-7e60-a385-ba8663e2825d" xlink:to="loc_us-gaap_Depreciation_019cb481-9e6f-7cb9-a607-787bf30cc91d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentNet_019cb481-9e6f-78e4-bddd-40371948169c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019cb481-9e6f-7e60-a385-ba8663e2825d" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentNet_019cb481-9e6f-78e4-bddd-40371948169c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetRetirementObligation_019cb481-9e6f-7e0d-b370-823a12d70b1a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetRetirementObligation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PropertyPlantAndEquipmentLineItems_019cb481-9e6f-7e60-a385-ba8663e2825d" xlink:to="loc_us-gaap_AssetRetirementObligation_019cb481-9e6f-7e0d-b370-823a12d70b1a" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/GOODWILLANDINTANGIBLEASSETSNarrativeDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#GOODWILLANDINTANGIBLEASSETSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/GOODWILLANDINTANGIBLEASSETSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-710c-9d55-64e990f22891" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_019cb481-9e6f-7e0d-b854-091970b2da51" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-710c-9d55-64e990f22891" xlink:to="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_019cb481-9e6f-7e0d-b854-091970b2da51" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019d1f89-93a1-72e8-b24b-d1f1d3ad5637" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_019cb481-9e6f-7e0d-b854-091970b2da51" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019d1f89-93a1-72e8-b24b-d1f1d3ad5637" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d1f89-93a1-72e8-b24b-d1f1d3ad5637_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019d1f89-93a1-72e8-b24b-d1f1d3ad5637" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d1f89-93a1-72e8-b24b-d1f1d3ad5637_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d1f89-93a1-74d2-9684-522cba0f445e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019d1f89-93a1-72e8-b24b-d1f1d3ad5637" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d1f89-93a1-74d2-9684-522cba0f445e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_GQBioAcquisitionMember_019d1f89-93a2-7556-80cf-8e1a1dea5500" xlink:href="pcrx-20260331.xsd#pcrx_GQBioAcquisitionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d1f89-93a1-74d2-9684-522cba0f445e" xlink:to="loc_pcrx_GQBioAcquisitionMember_019d1f89-93a2-7556-80cf-8e1a1dea5500" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_Goodwill_019d1f89-5b8e-76dd-86db-d6bac34cd7a8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_Goodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-710c-9d55-64e990f22891" xlink:to="loc_us-gaap_Goodwill_019d1f89-5b8e-76dd-86db-d6bac34cd7a8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_019d1f89-5b8e-729b-b053-273cc3e85a83" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillForeignCurrencyTranslationGainLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-710c-9d55-64e990f22891" xlink:to="loc_us-gaap_GoodwillForeignCurrencyTranslationGainLoss_019d1f89-5b8e-729b-b053-273cc3e85a83" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GoodwillImpairmentLoss_019d1f89-5b8e-7e6e-8fdd-cacf5f758581" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GoodwillImpairmentLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-710c-9d55-64e990f22891" xlink:to="loc_us-gaap_GoodwillImpairmentLoss_019d1f89-5b8e-7e6e-8fdd-cacf5f758581" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_019d1f89-93a2-75e7-9c86-7ee2d18a019a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-710c-9d55-64e990f22891" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_019d1f89-93a2-75e7-9c86-7ee2d18a019a" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_019d1f89-93a2-70af-a55a-13baece20c7d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-710c-9d55-64e990f22891" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseRemainderOfFiscalYear_019d1f89-93a2-70af-a55a-13baece20c7d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_019d1f89-93a2-7e5a-8fb4-1dcd641b9cb0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-710c-9d55-64e990f22891" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths_019d1f89-93a2-7e5a-8fb4-1dcd641b9cb0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_019d1f89-93a2-70a2-b264-11b75ca9b03b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-710c-9d55-64e990f22891" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo_019d1f89-93a2-70a2-b264-11b75ca9b03b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_019d1f89-93a2-7469-93de-5ffb4b99abd4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-710c-9d55-64e990f22891" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree_019d1f89-93a2-7469-93de-5ffb4b99abd4" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_019d1f89-93a2-76ae-9895-1465d319d99d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-710c-9d55-64e990f22891" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour_019d1f89-93a2-76ae-9895-1465d319d99d" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_019d1f89-93a2-7ee5-9a15-f763623844ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-710c-9d55-64e990f22891" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive_019d1f89-93a2-7ee5-9a15-f763623844ea" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_FiniteLivedIntangibleAssetExpectedAmortizationYearSix_019d1f89-93a2-7dfc-8709-900c42147947" xlink:href="pcrx-20260331.xsd#pcrx_FiniteLivedIntangibleAssetExpectedAmortizationYearSix"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-710c-9d55-64e990f22891" xlink:to="loc_pcrx_FiniteLivedIntangibleAssetExpectedAmortizationYearSix_019d1f89-93a2-7dfc-8709-900c42147947" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_FiniteLivedIntangibleAssetExpectedAmortizationYearSeven_019d1f89-93a2-7a69-8452-aea79010618a" xlink:href="pcrx-20260331.xsd#pcrx_FiniteLivedIntangibleAssetExpectedAmortizationYearSeven"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-710c-9d55-64e990f22891" xlink:to="loc_pcrx_FiniteLivedIntangibleAssetExpectedAmortizationYearSeven_019d1f89-93a2-7a69-8452-aea79010618a" xlink:type="arc" order="11"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/GOODWILLANDINTANGIBLEASSETSScheduleofFiniteLivedIntangibleAssetsAcquiredasPartofBusinessCombinationDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#GOODWILLANDINTANGIBLEASSETSScheduleofFiniteLivedIntangibleAssetsAcquiredasPartofBusinessCombinationDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/GOODWILLANDINTANGIBLEASSETSScheduleofFiniteLivedIntangibleAssetsAcquiredasPartofBusinessCombinationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-7cd8-b24c-d971bbd83dc9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_019cb481-9e6f-73a9-8e71-66a75c242c2e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-7cd8-b24c-d971bbd83dc9" xlink:to="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_019cb481-9e6f-73a9-8e71-66a75c242c2e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cb481-9e6f-74f7-a1d0-369e9ec20c46" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_019cb481-9e6f-73a9-8e71-66a75c242c2e" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cb481-9e6f-74f7-a1d0-369e9ec20c46" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cb481-9e6f-74f7-a1d0-369e9ec20c46_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cb481-9e6f-74f7-a1d0-369e9ec20c46" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cb481-9e6f-74f7-a1d0-369e9ec20c46_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cb481-9e6f-7f7f-adcc-e7bcb2b3a147" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis_019cb481-9e6f-74f7-a1d0-369e9ec20c46" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cb481-9e6f-7f7f-adcc-e7bcb2b3a147" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DevelopedTechnologyRightsMember_019cb481-9e6f-799f-9489-84f97a26ce76" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DevelopedTechnologyRightsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cb481-9e6f-7f7f-adcc-e7bcb2b3a147" xlink:to="loc_us-gaap_DevelopedTechnologyRightsMember_019cb481-9e6f-799f-9489-84f97a26ce76" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerRelationshipsMember_019cb481-9e6f-71a5-b518-0de67ad21d6f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerRelationshipsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FiniteLivedIntangibleAssetsMajorClassNameDomain_019cb481-9e6f-7f7f-adcc-e7bcb2b3a147" xlink:to="loc_us-gaap_CustomerRelationshipsMember_019cb481-9e6f-71a5-b518-0de67ad21d6f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019cb481-9e6f-7779-a1a8-92b75647ddf7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAcquiredFiniteLivedIntangibleAssetByMajorClassTable_019cb481-9e6f-73a9-8e71-66a75c242c2e" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019cb481-9e6f-7779-a1a8-92b75647ddf7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019cb481-9e6f-7779-a1a8-92b75647ddf7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019cb481-9e6f-7779-a1a8-92b75647ddf7" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019cb481-9e6f-7779-a1a8-92b75647ddf7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019cb481-9e6f-7470-b028-3f3ca531f634" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsByMajorClassAxis_019cb481-9e6f-7779-a1a8-92b75647ddf7" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019cb481-9e6f-7470-b028-3f3ca531f634" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InProcessResearchAndDevelopmentMember_019cb481-9e6f-7cfb-97eb-5154e5a3fab4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InProcessResearchAndDevelopmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IndefiniteLivedIntangibleAssetsMajorClassNameDomain_019cb481-9e6f-7470-b028-3f3ca531f634" xlink:to="loc_us-gaap_InProcessResearchAndDevelopmentMember_019cb481-9e6f-7cfb-97eb-5154e5a3fab4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019cb481-9e6f-72f8-bcac-dce7135d6ec6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-7cd8-b24c-d971bbd83dc9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsGross_019cb481-9e6f-72f8-bcac-dce7135d6ec6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019cb481-9e6f-7336-a36c-e58e532d1128" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-7cd8-b24c-d971bbd83dc9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization_019cb481-9e6f-7336-a36c-e58e532d1128" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019cb481-9e6f-7f79-8564-a32d2d8f6ca0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FiniteLivedIntangibleAssetsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-7cd8-b24c-d971bbd83dc9" xlink:to="loc_us-gaap_FiniteLivedIntangibleAssetsNet_019cb481-9e6f-7f79-8564-a32d2d8f6ca0" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_019cb481-9e6f-74eb-890f-14e019bc53f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-7cd8-b24c-d971bbd83dc9" xlink:to="loc_us-gaap_IndefiniteLivedIntangibleAssetsExcludingGoodwill_019cb481-9e6f-74eb-890f-14e019bc53f9" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_019cb481-9e6f-79d5-8fed-093aa25a178d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsGrossExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-7cd8-b24c-d971bbd83dc9" xlink:to="loc_us-gaap_IntangibleAssetsGrossExcludingGoodwill_019cb481-9e6f-79d5-8fed-093aa25a178d" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019cb481-9e6f-749f-9eb1-68949d79e439" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IntangibleAssetsNetExcludingGoodwill"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-7cd8-b24c-d971bbd83dc9" xlink:to="loc_us-gaap_IntangibleAssetsNetExcludingGoodwill_019cb481-9e6f-749f-9eb1-68949d79e439" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_019cb481-9e6f-7392-8820-e961053796d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsLineItems_019cb481-9e6f-7cd8-b24c-d971bbd83dc9" xlink:to="loc_us-gaap_AcquiredFiniteLivedIntangibleAssetsWeightedAverageUsefulLife_019cb481-9e6f-7392-8820-e961053796d6" xlink:type="arc" order="6"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/DEBTScheduleofLongTermDebtInstrumentsDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#DEBTScheduleofLongTermDebtInstrumentsDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/DEBTScheduleofLongTermDebtInstrumentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019cb481-9e6f-7beb-8e89-283351cf81ad" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-7362-8730-d0c3672a08f7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9e6f-7beb-8e89-283351cf81ad" xlink:to="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-7362-8730-d0c3672a08f7" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019cb481-9e6f-77dc-ad04-75132bb52dc7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-7362-8730-d0c3672a08f7" xlink:to="loc_us-gaap_DebtInstrumentAxis_019cb481-9e6f-77dc-ad04-75132bb52dc7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019cb481-9e6f-77dc-ad04-75132bb52dc7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019cb481-9e6f-77dc-ad04-75132bb52dc7" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019cb481-9e6f-77dc-ad04-75132bb52dc7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019cb481-9e6f-71c2-aba3-0fe5a6f6f5eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019cb481-9e6f-77dc-ad04-75132bb52dc7" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019cb481-9e6f-71c2-aba3-0fe5a6f6f5eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ConvertibleSeniorNotesDue2029Member_019cb481-9e6f-7162-94b9-7e1df52f2a92" xlink:href="pcrx-20260331.xsd#pcrx_ConvertibleSeniorNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cb481-9e6f-71c2-aba3-0fe5a6f6f5eb" xlink:to="loc_pcrx_ConvertibleSeniorNotesDue2029Member_019cb481-9e6f-7162-94b9-7e1df52f2a92" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019cb481-9e6f-7108-a82d-ee647977d1f2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-7362-8730-d0c3672a08f7" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019cb481-9e6f-7108-a82d-ee647977d1f2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9e6f-7108-a82d-ee647977d1f2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019cb481-9e6f-7108-a82d-ee647977d1f2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9e6f-7108-a82d-ee647977d1f2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9e6f-7df8-9673-efbfaefedf61" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019cb481-9e6f-7108-a82d-ee647977d1f2" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9e6f-7df8-9673-efbfaefedf61" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_019cb481-9e6f-7e3d-b938-844c62993cf5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9e6f-7df8-9673-efbfaefedf61" xlink:to="loc_us-gaap_UnsecuredDebtMember_019cb481-9e6f-7e3d-b938-844c62993cf5" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019cb481-9e6f-7b8f-9389-bd163820b625" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9e6f-7df8-9673-efbfaefedf61" xlink:to="loc_us-gaap_LineOfCreditMember_019cb481-9e6f-7b8f-9389-bd163820b625" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019cb481-9e6f-718b-9673-7883e5caa4a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-7362-8730-d0c3672a08f7" xlink:to="loc_us-gaap_CreditFacilityAxis_019cb481-9e6f-718b-9673-7883e5caa4a1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019cb481-9e6f-718b-9673-7883e5caa4a1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019cb481-9e6f-718b-9673-7883e5caa4a1" xlink:to="loc_us-gaap_CreditFacilityDomain_019cb481-9e6f-718b-9673-7883e5caa4a1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019cb481-9e6f-7093-91f5-367c46ce133c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019cb481-9e6f-718b-9673-7883e5caa4a1" xlink:to="loc_us-gaap_CreditFacilityDomain_019cb481-9e6f-7093-91f5-367c46ce133c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019cb481-9e6f-7283-a1c1-9324d8db1488" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019cb481-9e6f-7093-91f5-367c46ce133c" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019cb481-9e6f-7283-a1c1-9324d8db1488" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019cb481-9e6f-7eb1-83d5-044104e13584" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9e6f-7beb-8e89-283351cf81ad" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019cb481-9e6f-7eb1-83d5-044104e13584" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019cb481-9e6f-7477-89e2-6dca9688f23c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9e6f-7beb-8e89-283351cf81ad" xlink:to="loc_us-gaap_LongTermDebt_019cb481-9e6f-7477-89e2-6dca9688f23c" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/DEBTNarrativeDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#DEBTNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/DEBTNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-76fe-94e5-d5f8e748bb66" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-76fe-94e5-d5f8e748bb66" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019dadfe-f421-79a4-8974-d156f809f6cf" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-76fe-94e5-d5f8e748bb66" xlink:to="loc_us-gaap_DebtInstrumentAxis_019dadfe-f421-79a4-8974-d156f809f6cf" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dadfe-f421-79a4-8974-d156f809f6cf_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dadfe-f421-79a4-8974-d156f809f6cf" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dadfe-f421-79a4-8974-d156f809f6cf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019dadfe-f421-7f4c-a671-797cec32810f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019dadfe-f421-79a4-8974-d156f809f6cf" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019dadfe-f421-7f4c-a671-797cec32810f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ConvertibleSeniorNotesDue2029Member_019dadfe-f421-7039-a983-e535f95fd637" xlink:href="pcrx-20260331.xsd#pcrx_ConvertibleSeniorNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dadfe-f421-7f4c-a671-797cec32810f" xlink:to="loc_pcrx_ConvertibleSeniorNotesDue2029Member_019dadfe-f421-7039-a983-e535f95fd637" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_WellsFargoBankNationalAssociationCreditAgreementMember_019dae01-1aab-79a2-8688-4dbf371685f3" xlink:href="pcrx-20260331.xsd#pcrx_WellsFargoBankNationalAssociationCreditAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dadfe-f421-7f4c-a671-797cec32810f" xlink:to="loc_pcrx_WellsFargoBankNationalAssociationCreditAgreementMember_019dae01-1aab-79a2-8688-4dbf371685f3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_TermLoanAFacilityDueMarch2028Member_019dae01-6acb-73c6-98fe-168183206ab2" xlink:href="pcrx-20260331.xsd#pcrx_TermLoanAFacilityDueMarch2028Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dadfe-f421-7f4c-a671-797cec32810f" xlink:to="loc_pcrx_TermLoanAFacilityDueMarch2028Member_019dae01-6acb-73c6-98fe-168183206ab2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ConvertibleSeniorNotesDue2025Member_019dae01-88ca-78fa-991d-db4812ab3857" xlink:href="pcrx-20260331.xsd#pcrx_ConvertibleSeniorNotesDue2025Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019dadfe-f421-7f4c-a671-797cec32810f" xlink:to="loc_pcrx_ConvertibleSeniorNotesDue2025Member_019dae01-88ca-78fa-991d-db4812ab3857" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019dadfe-f421-71a4-a263-06ab46771822" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-76fe-94e5-d5f8e748bb66" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019dadfe-f421-71a4-a263-06ab46771822" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019dadfe-f421-71a4-a263-06ab46771822_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019dadfe-f421-71a4-a263-06ab46771822" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019dadfe-f421-71a4-a263-06ab46771822_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019dadfe-f421-799f-adbd-800d04fa027c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019dadfe-f421-71a4-a263-06ab46771822" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019dadfe-f421-799f-adbd-800d04fa027c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_019dadfe-f421-7b16-9eb0-ba660592bc3e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dadfe-f421-799f-adbd-800d04fa027c" xlink:to="loc_us-gaap_UnsecuredDebtMember_019dadfe-f421-7b16-9eb0-ba660592bc3e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConvertibleDebtMember_019dae01-1aab-7d13-b0c9-594737e348b8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConvertibleDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dadfe-f421-799f-adbd-800d04fa027c" xlink:to="loc_us-gaap_ConvertibleDebtMember_019dae01-1aab-7d13-b0c9-594737e348b8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019dae01-1aab-76a6-ba5e-05bce7cc5026" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dadfe-f421-799f-adbd-800d04fa027c" xlink:to="loc_us-gaap_LineOfCreditMember_019dae01-1aab-76a6-ba5e-05bce7cc5026" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredDebtMember_019dae01-6acb-7a6e-a21a-056525f88618" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019dadfe-f421-799f-adbd-800d04fa027c" xlink:to="loc_us-gaap_SecuredDebtMember_019dae01-6acb-7a6e-a21a-056525f88618" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DebtInstrumentConvertibleTermsOfConversionAxis_019dadff-79a5-7037-a67b-afce506d8dbc" xlink:href="pcrx-20260331.xsd#pcrx_DebtInstrumentConvertibleTermsOfConversionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-76fe-94e5-d5f8e748bb66" xlink:to="loc_pcrx_DebtInstrumentConvertibleTermsOfConversionAxis_019dadff-79a5-7037-a67b-afce506d8dbc" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DebtInstrumentConvertibleTermsOfConversionDomain_019dadff-79a5-7037-a67b-afce506d8dbc_default" xlink:href="pcrx-20260331.xsd#pcrx_DebtInstrumentConvertibleTermsOfConversionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pcrx_DebtInstrumentConvertibleTermsOfConversionAxis_019dadff-79a5-7037-a67b-afce506d8dbc" xlink:to="loc_pcrx_DebtInstrumentConvertibleTermsOfConversionDomain_019dadff-79a5-7037-a67b-afce506d8dbc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DebtInstrumentConvertibleTermsOfConversionDomain_019dadff-79a5-78f1-aefd-f09c1148fce2" xlink:href="pcrx-20260331.xsd#pcrx_DebtInstrumentConvertibleTermsOfConversionDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pcrx_DebtInstrumentConvertibleTermsOfConversionAxis_019dadff-79a5-7037-a67b-afce506d8dbc" xlink:to="loc_pcrx_DebtInstrumentConvertibleTermsOfConversionDomain_019dadff-79a5-78f1-aefd-f09c1148fce2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DebtConversionTermsOneMember_019dadff-79a5-78f3-a06d-53c774f82e43" xlink:href="pcrx-20260331.xsd#pcrx_DebtConversionTermsOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pcrx_DebtInstrumentConvertibleTermsOfConversionDomain_019dadff-79a5-78f1-aefd-f09c1148fce2" xlink:to="loc_pcrx_DebtConversionTermsOneMember_019dadff-79a5-78f3-a06d-53c774f82e43" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DebtConversionTermsTwoMember_019dadff-79a5-7be3-abc4-b6d8a8cd1086" xlink:href="pcrx-20260331.xsd#pcrx_DebtConversionTermsTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pcrx_DebtInstrumentConvertibleTermsOfConversionDomain_019dadff-79a5-78f1-aefd-f09c1148fce2" xlink:to="loc_pcrx_DebtConversionTermsTwoMember_019dadff-79a5-7be3-abc4-b6d8a8cd1086" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DebtConversionTermsThreeMember_019dae00-e6cd-78a2-befe-1f6f01fb86ab" xlink:href="pcrx-20260331.xsd#pcrx_DebtConversionTermsThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pcrx_DebtInstrumentConvertibleTermsOfConversionDomain_019dadff-79a5-78f1-aefd-f09c1148fce2" xlink:to="loc_pcrx_DebtConversionTermsThreeMember_019dae00-e6cd-78a2-befe-1f6f01fb86ab" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeInstrumentRiskAxis_019dae01-1aab-7f74-903e-fe619823d113" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeInstrumentRiskAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-76fe-94e5-d5f8e748bb66" xlink:to="loc_us-gaap_DerivativeInstrumentRiskAxis_019dae01-1aab-7f74-903e-fe619823d113" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dae01-1aab-7f74-903e-fe619823d113_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dae01-1aab-7f74-903e-fe619823d113" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dae01-1aab-7f74-903e-fe619823d113_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DerivativeContractTypeDomain_019dae01-1aab-7402-a825-bfdb27d0bbe3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DerivativeContractTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DerivativeInstrumentRiskAxis_019dae01-1aab-7f74-903e-fe619823d113" xlink:to="loc_us-gaap_DerivativeContractTypeDomain_019dae01-1aab-7402-a825-bfdb27d0bbe3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_CappedCallMember_019dae01-1aab-7649-a136-7cfa124d17d9" xlink:href="pcrx-20260331.xsd#pcrx_CappedCallMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DerivativeContractTypeDomain_019dae01-1aab-7402-a825-bfdb27d0bbe3" xlink:to="loc_pcrx_CappedCallMember_019dae01-1aab-7649-a136-7cfa124d17d9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019dae01-1aab-7e79-ab60-817a21a47d81" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-76fe-94e5-d5f8e748bb66" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019dae01-1aab-7e79-ab60-817a21a47d81" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dae01-1aab-7e79-ab60-817a21a47d81_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dae01-1aab-7e79-ab60-817a21a47d81" xlink:to="loc_us-gaap_EquityComponentDomain_019dae01-1aab-7e79-ab60-817a21a47d81_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019dae01-1aab-778c-9a82-f07aa2e39864" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019dae01-1aab-7e79-ab60-817a21a47d81" xlink:to="loc_us-gaap_EquityComponentDomain_019dae01-1aab-778c-9a82-f07aa2e39864" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AdditionalPaidInCapitalMember_019dae01-1aab-764c-8289-8b4eded6c901" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AdditionalPaidInCapitalMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019dae01-1aab-778c-9a82-f07aa2e39864" xlink:to="loc_us-gaap_AdditionalPaidInCapitalMember_019dae01-1aab-764c-8289-8b4eded6c901" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019dae01-1aab-7965-9b29-df954e2af9ba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-76fe-94e5-d5f8e748bb66" xlink:to="loc_us-gaap_CreditFacilityAxis_019dae01-1aab-7965-9b29-df954e2af9ba" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019dae01-1aab-7965-9b29-df954e2af9ba_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019dae01-1aab-7965-9b29-df954e2af9ba" xlink:to="loc_us-gaap_CreditFacilityDomain_019dae01-1aab-7965-9b29-df954e2af9ba_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019dae01-1aab-75b2-bd37-95593cd7d47f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019dae01-1aab-7965-9b29-df954e2af9ba" xlink:to="loc_us-gaap_CreditFacilityDomain_019dae01-1aab-75b2-bd37-95593cd7d47f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019dae01-1aab-7a88-a327-b8abdb2fb167" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019dae01-1aab-75b2-bd37-95593cd7d47f" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019dae01-1aab-7a88-a327-b8abdb2fb167" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LetterOfCreditMember_019dae01-1aab-7516-87ca-5f5c3ab625ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LetterOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019dae01-1aab-75b2-bd37-95593cd7d47f" xlink:to="loc_us-gaap_LetterOfCreditMember_019dae01-1aab-7516-87ca-5f5c3ab625ab" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BridgeLoanMember_019dae01-1aab-7b66-835a-3f46ae30ebc8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BridgeLoanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019dae01-1aab-75b2-bd37-95593cd7d47f" xlink:to="loc_us-gaap_BridgeLoanMember_019dae01-1aab-7b66-835a-3f46ae30ebc8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019dae01-4412-7458-ab0d-dd8fd47c00cf" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-76fe-94e5-d5f8e748bb66" xlink:to="loc_srt_RangeAxis_019dae01-4412-7458-ab0d-dd8fd47c00cf" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019dae01-4412-7458-ab0d-dd8fd47c00cf_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019dae01-4412-7458-ab0d-dd8fd47c00cf" xlink:to="loc_srt_RangeMember_019dae01-4412-7458-ab0d-dd8fd47c00cf_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019dae01-4412-7bee-a5a5-ede1f8c0c77e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019dae01-4412-7458-ab0d-dd8fd47c00cf" xlink:to="loc_srt_RangeMember_019dae01-4412-7bee-a5a5-ede1f8c0c77e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019dae01-4412-773b-b010-949973e6f582" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019dae01-4412-7bee-a5a5-ede1f8c0c77e" xlink:to="loc_srt_MinimumMember_019dae01-4412-773b-b010-949973e6f582" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019dae01-4412-746e-b5bf-f2c2cb6a556d" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019dae01-4412-7bee-a5a5-ede1f8c0c77e" xlink:to="loc_srt_MaximumMember_019dae01-4412-746e-b5bf-f2c2cb6a556d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateAxis_019dae01-4412-733c-9b08-03cacfbe525e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-76fe-94e5-d5f8e748bb66" xlink:to="loc_us-gaap_VariableRateAxis_019dae01-4412-733c-9b08-03cacfbe525e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019dae01-4412-733c-9b08-03cacfbe525e_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_VariableRateAxis_019dae01-4412-733c-9b08-03cacfbe525e" xlink:to="loc_us-gaap_VariableRateDomain_019dae01-4412-733c-9b08-03cacfbe525e_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_VariableRateDomain_019dae01-4412-7d31-9c8a-6182f0fb00ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_VariableRateDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_VariableRateAxis_019dae01-4412-733c-9b08-03cacfbe525e" xlink:to="loc_us-gaap_VariableRateDomain_019dae01-4412-7d31-9c8a-6182f0fb00ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BaseRateMember_019dae01-4412-77ce-bfeb-1b197e47bc71" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BaseRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019dae01-4412-7d31-9c8a-6182f0fb00ea" xlink:to="loc_us-gaap_BaseRateMember_019dae01-4412-77ce-bfeb-1b197e47bc71" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019dae01-4412-7ca5-8cfc-220e26a76b01" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SecuredOvernightFinancingRateSofrMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_VariableRateDomain_019dae01-4412-7d31-9c8a-6182f0fb00ea" xlink:to="loc_us-gaap_SecuredOvernightFinancingRateSofrMember_019dae01-4412-7ca5-8cfc-220e26a76b01" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementScenarioAxis_019dae01-6acb-77d0-80e9-8918c72bd5db" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementScenarioAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cb481-9e6f-76fe-94e5-d5f8e748bb66" xlink:to="loc_srt_StatementScenarioAxis_019dae01-6acb-77d0-80e9-8918c72bd5db" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dae01-6acb-77d0-80e9-8918c72bd5db_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementScenarioAxis_019dae01-6acb-77d0-80e9-8918c72bd5db" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dae01-6acb-77d0-80e9-8918c72bd5db_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioUnspecifiedDomain_019dae01-6acb-77b1-9a1e-0aa856e4bf2c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioUnspecifiedDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementScenarioAxis_019dae01-6acb-77d0-80e9-8918c72bd5db" xlink:to="loc_srt_ScenarioUnspecifiedDomain_019dae01-6acb-77b1-9a1e-0aa856e4bf2c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ScenarioForecastMember_019dae01-6acb-7f49-b870-5c4c4dc76d2a" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ScenarioForecastMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ScenarioUnspecifiedDomain_019dae01-6acb-77b1-9a1e-0aa856e4bf2c" xlink:to="loc_srt_ScenarioForecastMember_019dae01-6acb-7f49-b870-5c4c4dc76d2a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFaceAmount_019dadfe-f421-788f-9ac6-c46a034439e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtInstrumentFaceAmount_019dadfe-f421-788f-9ac6-c46a034439e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dadfe-f421-7d49-8fd3-54fe7dec900e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019dadfe-f421-7d49-8fd3-54fe7dec900e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DebtInstrumentMarketPrice_019dadff-288e-76df-99cc-e36d36826ea6" xlink:href="pcrx-20260331.xsd#pcrx_DebtInstrumentMarketPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_pcrx_DebtInstrumentMarketPrice_019dadff-288e-76df-99cc-e36d36826ea6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DebtInstrumentRepurchasedInConversionFaceAmount_019dadff-79a5-71ba-a281-32c33bbd5e10" xlink:href="pcrx-20260331.xsd#pcrx_DebtInstrumentRepurchasedInConversionFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_pcrx_DebtInstrumentRepurchasedInConversionFaceAmount_019dadff-79a5-71ba-a281-32c33bbd5e10" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_019dadff-79a5-7796-a155-4c2923fa39b3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentConvertibleThresholdTradingDays"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdTradingDays_019dadff-79a5-7796-a155-4c2923fa39b3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_019dadff-79a5-7345-89bc-c23adfaddc2d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdConsecutiveTradingDays1_019dadff-79a5-7345-89bc-c23adfaddc2d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_019dadff-79a5-7af0-97d5-ec548ec43c12" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtInstrumentConvertibleThresholdPercentageOfStockPriceTrigger_019dadff-79a5-7af0-97d5-ec548ec43c12" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DebtInstrumentConvertibleThresholdPercentageOfStockTradingPrice_019dadff-79a5-7a99-a2aa-510c457e8ddf" xlink:href="pcrx-20260331.xsd#pcrx_DebtInstrumentConvertibleThresholdPercentageOfStockTradingPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_pcrx_DebtInstrumentConvertibleThresholdPercentageOfStockTradingPrice_019dadff-79a5-7a99-a2aa-510c457e8ddf" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_SettlementPeriodConvertibleDebtConversionRequest_019dadff-a6c5-7da4-9ef1-684b44e25530" xlink:href="pcrx-20260331.xsd#pcrx_SettlementPeriodConvertibleDebtConversionRequest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_pcrx_SettlementPeriodConvertibleDebtConversionRequest_019dadff-a6c5-7da4-9ef1-684b44e25530" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_019dae00-354c-7457-887d-6135c1c8c040" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentConvertibleConversionRatio1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionRatio1_019dae00-354c-7457-887d-6135c1c8c040" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_019dae00-e6cd-7175-b37e-dec0c9a5753d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_019dae00-e6cd-7175-b37e-dec0c9a5753d" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DebtInstrumentConversionObligationPremiumOnCommonStock_019dae00-e6cd-7ee3-8ab4-41240a5aaf0e" xlink:href="pcrx-20260331.xsd#pcrx_DebtInstrumentConversionObligationPremiumOnCommonStock"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_pcrx_DebtInstrumentConversionObligationPremiumOnCommonStock_019dae00-e6cd-7ee3-8ab4-41240a5aaf0e" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharePrice_019dae00-e6cd-78ec-9958-18c616010b9c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_SharePrice_019dae00-e6cd-78ec-9958-18c616010b9c" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DebtInstrumentConvertibleRedemptionTradingDaysFromMaturity_019dae00-e6cd-754a-8337-343e5060af76" xlink:href="pcrx-20260331.xsd#pcrx_DebtInstrumentConvertibleRedemptionTradingDaysFromMaturity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_pcrx_DebtInstrumentConvertibleRedemptionTradingDaysFromMaturity_019dae00-e6cd-754a-8337-343e5060af76" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_019dae00-e6cd-7e7e-96a5-5829e4740d3d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentRedemptionPricePercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtInstrumentRedemptionPricePercentage_019dae00-e6cd-7e7e-96a5-5829e4740d3d" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DerivativeCappedCallPrice_019dae01-1aab-7861-a83e-e30c6917ff65" xlink:href="pcrx-20260331.xsd#pcrx_DerivativeCappedCallPrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_pcrx_DerivativeCappedCallPrice_019dae01-1aab-7861-a83e-e30c6917ff65" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DerivativePremiumPercentage_019dae01-1aab-7652-94af-5f1cd4b89c3c" xlink:href="pcrx-20260331.xsd#pcrx_DerivativePremiumPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_pcrx_DerivativePremiumPercentage_019dae01-1aab-7652-94af-5f1cd4b89c3c" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_AdjustmentsToAdditionalPaidInCapitalPurchaseOfCappedCallsBeforeTax_019dae01-1aab-7bdb-94e3-ded1150ba7ea" xlink:href="pcrx-20260331.xsd#pcrx_AdjustmentsToAdditionalPaidInCapitalPurchaseOfCappedCallsBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_pcrx_AdjustmentsToAdditionalPaidInCapitalPurchaseOfCappedCallsBeforeTax_019dae01-1aab-7bdb-94e3-ded1150ba7ea" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_AdjustmentsToAdditionalPaidInCapitalPurchaseOfCappedCallsTax_019dae01-1aab-74b1-a66d-b53ec9becb95" xlink:href="pcrx-20260331.xsd#pcrx_AdjustmentsToAdditionalPaidInCapitalPurchaseOfCappedCallsTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_pcrx_AdjustmentsToAdditionalPaidInCapitalPurchaseOfCappedCallsTax_019dae01-1aab-74b1-a66d-b53ec9becb95" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019dae01-1aab-7081-82a0-01765ca792fe" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_LineOfCreditFacilityMaximumBorrowingCapacity_019dae01-1aab-7081-82a0-01765ca792fe" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DebtInstrumentCovenantIncrementalDebtMaximum_019dae01-1aab-76c5-860c-417975dbb0e1" xlink:href="pcrx-20260331.xsd#pcrx_DebtInstrumentCovenantIncrementalDebtMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_pcrx_DebtInstrumentCovenantIncrementalDebtMaximum_019dae01-1aab-76c5-860c-417975dbb0e1" xlink:type="arc" order="20"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DebtInstrumentCovenantIncrementalDebtMaximumPercent_019dae01-1aab-79bb-b3ce-b244c36ee95e" xlink:href="pcrx-20260331.xsd#pcrx_DebtInstrumentCovenantIncrementalDebtMaximumPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_pcrx_DebtInstrumentCovenantIncrementalDebtMaximumPercent_019dae01-1aab-79bb-b3ce-b244c36ee95e" xlink:type="arc" order="21"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019dae01-4412-7cfe-bcdc-4ccdc66f5ecc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentBasisSpreadOnVariableRate1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtInstrumentBasisSpreadOnVariableRate1_019dae01-4412-7cfe-bcdc-4ccdc66f5ecc" xlink:type="arc" order="22"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet_019dae01-4412-7244-8a59-059dd4c12808" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtIssuanceCostsLineOfCreditArrangementsNet_019dae01-4412-7244-8a59-059dd4c12808" xlink:type="arc" order="23"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLongTermLinesOfCredit_019dae01-4412-7680-8094-77104353fc69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromLongTermLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_ProceedsFromLongTermLinesOfCredit_019dae01-4412-7680-8094-77104353fc69" xlink:type="arc" order="24"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCredit_019dae01-4412-7453-8b22-468ed7113542" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_LineOfCredit_019dae01-4412-7453-8b22-468ed7113542" xlink:type="arc" order="25"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentPeriodicPaymentPrincipal_019dae01-4412-7afd-91b9-830adf2f2d09" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentPeriodicPaymentPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtInstrumentPeriodicPaymentPrincipal_019dae01-4412-7afd-91b9-830adf2f2d09" xlink:type="arc" order="26"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd_019dae01-4412-7a9c-abc0-97777b3004c2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_LineOfCreditFacilityInterestRateAtPeriodEnd_019dae01-4412-7a9c-abc0-97777b3004c2" xlink:type="arc" order="27"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DebtInstrumentDiscountRate_019dae01-6acb-7f5a-a6e8-83265fc3ebd5" xlink:href="pcrx-20260331.xsd#pcrx_DebtInstrumentDiscountRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_pcrx_DebtInstrumentDiscountRate_019dae01-6acb-7f5a-a6e8-83265fc3ebd5" xlink:type="arc" order="28"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLinesOfCredit_019dae01-6acb-77ab-8e20-a38d7c17023b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromLinesOfCredit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_ProceedsFromLinesOfCredit_019dae01-6acb-77ab-8e20-a38d7c17023b" xlink:type="arc" order="29"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentUnamortizedDiscount_019dae01-6acb-7bc6-8ea1-b9c7b2455826" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentUnamortizedDiscount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtInstrumentUnamortizedDiscount_019dae01-6acb-7bc6-8ea1-b9c7b2455826" xlink:type="arc" order="30"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaid_019dae01-6acb-746f-8596-7c7f0652915b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtInstrumentPeriodicPaymentTermsBalloonPaymentToBePaid_019dae01-6acb-746f-8596-7c7f0652915b" xlink:type="arc" order="31"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRepaidPrincipal_019dae01-6acb-7a84-b745-ba688ffe6240" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentRepaidPrincipal"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtInstrumentRepaidPrincipal_019dae01-6acb-7a84-b745-ba688ffe6240" xlink:type="arc" order="32"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestPaid_019dae01-6acb-7aeb-9c11-28e8229cf18c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestPaid"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_InterestPaid_019dae01-6acb-7aeb-9c11-28e8229cf18c" xlink:type="arc" order="33"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019dae01-6acb-7ab4-ac92-3459eb752db4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GainsLossesOnExtinguishmentOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_GainsLossesOnExtinguishmentOfDebt_019dae01-6acb-7ab4-ac92-3459eb752db4" xlink:type="arc" order="34"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfDebt_019dae01-6acb-76f3-a940-c64cbd5b73c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RepaymentsOfDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_RepaymentsOfDebt_019dae01-6acb-76f3-a940-c64cbd5b73c7" xlink:type="arc" order="35"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_019dae01-88ca-7721-af04-ad6e9a32be11" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentRepurchasedFaceAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_DebtInstrumentRepurchasedFaceAmount_019dae01-88ca-7721-af04-ad6e9a32be11" xlink:type="arc" order="36"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RepaymentsOfConvertibleDebt_019dae01-88ca-76a2-be14-6b361da9730b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RepaymentsOfConvertibleDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-7ba5-9f00-e9ee3b20d4fb" xlink:to="loc_us-gaap_RepaymentsOfConvertibleDebt_019dae01-88ca-76a2-be14-6b361da9730b" xlink:type="arc" order="37"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/DEBTScheduleofDebtDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#DEBTScheduleofDebtDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/DEBTScheduleofDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-70ee-88df-1f4059f815c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentTable_019cb481-9f12-7341-b9fc-22c668300ce5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-70ee-88df-1f4059f815c7" xlink:to="loc_us-gaap_DebtInstrumentTable_019cb481-9f12-7341-b9fc-22c668300ce5" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019cb481-9f12-7487-801f-8afe96aad40a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cb481-9f12-7341-b9fc-22c668300ce5" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019cb481-9f12-7487-801f-8afe96aad40a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9f12-7487-801f-8afe96aad40a_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019cb481-9f12-7487-801f-8afe96aad40a" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9f12-7487-801f-8afe96aad40a_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9f12-7a68-a13b-af381aa6b430" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019cb481-9f12-7487-801f-8afe96aad40a" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9f12-7a68-a13b-af381aa6b430" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_019cb481-9f12-7fde-b660-f981e4896985" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9f12-7a68-a13b-af381aa6b430" xlink:to="loc_us-gaap_UnsecuredDebtMember_019cb481-9f12-7fde-b660-f981e4896985" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019cb481-9f12-7c2d-b8fb-139fc0a0022d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_DebtInstrumentTable_019cb481-9f12-7341-b9fc-22c668300ce5" xlink:to="loc_us-gaap_DebtInstrumentAxis_019cb481-9f12-7c2d-b8fb-139fc0a0022d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019cb481-9f12-7c2d-b8fb-139fc0a0022d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019cb481-9f12-7c2d-b8fb-139fc0a0022d" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019cb481-9f12-7c2d-b8fb-139fc0a0022d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019cb481-9f12-7fc3-9ea4-f3efa30874eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019cb481-9f12-7c2d-b8fb-139fc0a0022d" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019cb481-9f12-7fc3-9ea4-f3efa30874eb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ConvertibleSeniorNotesDue2029Member_019cb481-9f12-7960-a28b-d3e9fbdabc07" xlink:href="pcrx-20260331.xsd#pcrx_ConvertibleSeniorNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cb481-9f12-7fc3-9ea4-f3efa30874eb" xlink:to="loc_pcrx_ConvertibleSeniorNotesDue2029Member_019cb481-9f12-7960-a28b-d3e9fbdabc07" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019cb481-9f12-7f3f-b18f-7c67e668fd18" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-70ee-88df-1f4059f815c7" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019cb481-9f12-7f3f-b18f-7c67e668fd18" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentCarryingAmount_019cb481-9f12-7292-b45b-a558548f578c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentCarryingAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-70ee-88df-1f4059f815c7" xlink:to="loc_us-gaap_DebtInstrumentCarryingAmount_019cb481-9f12-7292-b45b-a558548f578c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DeferredFinanceCostsNet_019cb481-9f12-7491-85f0-53297f4b8a4c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DeferredFinanceCostsNet"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-70ee-88df-1f4059f815c7" xlink:to="loc_us-gaap_DeferredFinanceCostsNet_019cb481-9f12-7491-85f0-53297f4b8a4c" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongTermDebt_019cb481-9f12-7514-918e-a001a41c9f82" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongTermDebt"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentLineItems_019cb481-9f12-70ee-88df-1f4059f815c7" xlink:to="loc_us-gaap_LongTermDebt_019cb481-9f12-7514-918e-a001a41c9f82" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/FINANCIALINSTRUMENTSScheduleofCarryingAmountandFairValueoftheLongTermDebtDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#FINANCIALINSTRUMENTSScheduleofCarryingAmountandFairValueoftheLongTermDebtDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/FINANCIALINSTRUMENTSScheduleofCarryingAmountandFairValueoftheLongTermDebtDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019cb481-9f12-7a9f-b9f1-51ad002e39c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019cb481-9f12-7a92-8f10-e55931fa4175" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByBalanceSheetGroupingTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019cb481-9f12-7a9f-b9f1-51ad002e39c5" xlink:to="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019cb481-9f12-7a92-8f10-e55931fa4175" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByMeasurementBasisAxis_019cb481-9f12-7bf7-8c8e-2037e6fe2844" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByMeasurementBasisAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019cb481-9f12-7a92-8f10-e55931fa4175" xlink:to="loc_us-gaap_FairValueByMeasurementBasisAxis_019cb481-9f12-7bf7-8c8e-2037e6fe2844" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019cb481-9f12-7bf7-8c8e-2037e6fe2844_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019cb481-9f12-7bf7-8c8e-2037e6fe2844" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019cb481-9f12-7bf7-8c8e-2037e6fe2844_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019cb481-9f12-7d70-92d0-b2e7521cefa3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueDisclosureItemAmountsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByMeasurementBasisAxis_019cb481-9f12-7bf7-8c8e-2037e6fe2844" xlink:to="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019cb481-9f12-7d70-92d0-b2e7521cefa3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019cb481-9f12-7429-a928-bc5212a802c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PortionAtFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueDisclosureItemAmountsDomain_019cb481-9f12-7d70-92d0-b2e7521cefa3" xlink:to="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019cb481-9f12-7429-a928-bc5212a802c0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019cb481-9f12-7851-a87f-1f06843a3075" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CarryingReportedAmountFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019cb481-9f12-7429-a928-bc5212a802c0" xlink:to="loc_us-gaap_CarryingReportedAmountFairValueDisclosureMember_019cb481-9f12-7851-a87f-1f06843a3075" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019cb481-9f12-79f1-a4c8-aeed6986b2ce" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EstimateOfFairValueFairValueDisclosureMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PortionAtFairValueFairValueDisclosureMember_019cb481-9f12-7429-a928-bc5212a802c0" xlink:to="loc_us-gaap_EstimateOfFairValueFairValueDisclosureMember_019cb481-9f12-79f1-a4c8-aeed6986b2ce" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cb481-9f12-7eac-8a15-a852a4a8e39d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019cb481-9f12-7a92-8f10-e55931fa4175" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cb481-9f12-7eac-8a15-a852a4a8e39d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-7eac-8a15-a852a4a8e39d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cb481-9f12-7eac-8a15-a852a4a8e39d" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-7eac-8a15-a852a4a8e39d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-7fc0-a014-6c9df535448a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cb481-9f12-7eac-8a15-a852a4a8e39d" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-7fc0-a014-6c9df535448a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel1Member_019cb481-9f12-7963-9450-a0217685b3bd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel1Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-7fc0-a014-6c9df535448a" xlink:to="loc_us-gaap_FairValueInputsLevel1Member_019cb481-9f12-7963-9450-a0217685b3bd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019cb481-9f12-7aa7-90ff-d889d1f2782c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-7fc0-a014-6c9df535448a" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019cb481-9f12-7aa7-90ff-d889d1f2782c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019cb481-9f12-7ac7-9021-b3dd3a454dcb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-7fc0-a014-6c9df535448a" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019cb481-9f12-7ac7-9021-b3dd3a454dcb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentAxis_019cb481-9f12-7810-a65b-fb4e645f7022" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019cb481-9f12-7a92-8f10-e55931fa4175" xlink:to="loc_us-gaap_DebtInstrumentAxis_019cb481-9f12-7810-a65b-fb4e645f7022" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019cb481-9f12-7810-a65b-fb4e645f7022_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_DebtInstrumentAxis_019cb481-9f12-7810-a65b-fb4e645f7022" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019cb481-9f12-7810-a65b-fb4e645f7022_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentNameDomain_019cb481-9f12-7d8b-bfd8-71b469172dcd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_DebtInstrumentAxis_019cb481-9f12-7810-a65b-fb4e645f7022" xlink:to="loc_us-gaap_DebtInstrumentNameDomain_019cb481-9f12-7d8b-bfd8-71b469172dcd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ConvertibleSeniorNotesDue2029Member_019cb481-9f12-7db7-85e7-4b0112ed1581" xlink:href="pcrx-20260331.xsd#pcrx_ConvertibleSeniorNotesDue2029Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_DebtInstrumentNameDomain_019cb481-9f12-7d8b-bfd8-71b469172dcd" xlink:to="loc_pcrx_ConvertibleSeniorNotesDue2029Member_019cb481-9f12-7db7-85e7-4b0112ed1581" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeAxis_019cb481-9f12-7f63-b512-1aeabdd32443" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019cb481-9f12-7a92-8f10-e55931fa4175" xlink:to="loc_us-gaap_LongtermDebtTypeAxis_019cb481-9f12-7f63-b512-1aeabdd32443" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9f12-7f63-b512-1aeabdd32443_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019cb481-9f12-7f63-b512-1aeabdd32443" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9f12-7f63-b512-1aeabdd32443_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9f12-71ed-b3c5-6a0b07daea60" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LongtermDebtTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_LongtermDebtTypeAxis_019cb481-9f12-7f63-b512-1aeabdd32443" xlink:to="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9f12-71ed-b3c5-6a0b07daea60" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_UnsecuredDebtMember_019cb481-9f12-720b-8588-ba16705c2efd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_UnsecuredDebtMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9f12-71ed-b3c5-6a0b07daea60" xlink:to="loc_us-gaap_UnsecuredDebtMember_019cb481-9f12-720b-8588-ba16705c2efd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LineOfCreditMember_019cb481-9f12-7f76-ae52-9abc9dfe9d6b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LineOfCreditMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LongtermDebtTypeDomain_019cb481-9f12-71ed-b3c5-6a0b07daea60" xlink:to="loc_us-gaap_LineOfCreditMember_019cb481-9f12-7f76-ae52-9abc9dfe9d6b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityAxis_019cb481-9f12-7203-be39-b55cf5fa514c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueByBalanceSheetGroupingTable_019cb481-9f12-7a92-8f10-e55931fa4175" xlink:to="loc_us-gaap_CreditFacilityAxis_019cb481-9f12-7203-be39-b55cf5fa514c" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019cb481-9f12-7203-be39-b55cf5fa514c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_CreditFacilityAxis_019cb481-9f12-7203-be39-b55cf5fa514c" xlink:to="loc_us-gaap_CreditFacilityDomain_019cb481-9f12-7203-be39-b55cf5fa514c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CreditFacilityDomain_019cb481-9f12-73b0-992f-7519d8964a6a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CreditFacilityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_CreditFacilityAxis_019cb481-9f12-7203-be39-b55cf5fa514c" xlink:to="loc_us-gaap_CreditFacilityDomain_019cb481-9f12-73b0-992f-7519d8964a6a" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevolvingCreditFacilityMember_019cb481-9f12-789d-b80d-9a192e020ab1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevolvingCreditFacilityMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_CreditFacilityDomain_019cb481-9f12-73b0-992f-7519d8964a6a" xlink:to="loc_us-gaap_RevolvingCreditFacilityMember_019cb481-9f12-789d-b80d-9a192e020ab1" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivablesFairValueDisclosureAbstract_019cb481-9f12-7944-bb36-6d59dfb0197b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReceivablesFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019cb481-9f12-7a9f-b9f1-51ad002e39c5" xlink:to="loc_us-gaap_ReceivablesFairValueDisclosureAbstract_019cb481-9f12-7944-bb36-6d59dfb0197b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_019cb481-9f12-7f0f-8701-ad5903456410" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivablesFairValueDisclosureAbstract_019cb481-9f12-7944-bb36-6d59dfb0197b" xlink:to="loc_us-gaap_EquitySecuritiesWithoutReadilyDeterminableFairValueAmount_019cb481-9f12-7f0f-8701-ad5903456410" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NotesReceivableFairValueDisclosure_019cb481-9f12-748c-a809-8fa86dce1c90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NotesReceivableFairValueDisclosure"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivablesFairValueDisclosureAbstract_019cb481-9f12-7944-bb36-6d59dfb0197b" xlink:to="loc_us-gaap_NotesReceivableFairValueDisclosure_019cb481-9f12-748c-a809-8fa86dce1c90" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialLiabilitiesFairValueDisclosureAbstract_019cb481-9f12-7a87-a6d2-5149421ba49c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialLiabilitiesFairValueDisclosureAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019cb481-9f12-7a9f-b9f1-51ad002e39c5" xlink:to="loc_us-gaap_FinancialLiabilitiesFairValueDisclosureAbstract_019cb481-9f12-7a87-a6d2-5149421ba49c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019cb481-9f12-775a-b8d2-c01ed374173c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FinancialLiabilitiesFairValueDisclosureAbstract_019cb481-9f12-7a87-a6d2-5149421ba49c" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019cb481-9f12-775a-b8d2-c01ed374173c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019cb481-9f12-718e-b7be-c65903bff637" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentInterestRateStatedPercentage"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019cb481-9f12-7a9f-b9f1-51ad002e39c5" xlink:to="loc_us-gaap_DebtInstrumentInterestRateStatedPercentage_019cb481-9f12-718e-b7be-c65903bff637" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentFairValue_019cb481-9f12-72b1-8b04-fa477a78cee0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019cb481-9f12-7a9f-b9f1-51ad002e39c5" xlink:to="loc_us-gaap_DebtInstrumentFairValue_019cb481-9f12-72b1-8b04-fa477a78cee0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharePrice_019cb481-9f12-7033-b1c6-e2e0d1d03768" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019cb481-9f12-7a9f-b9f1-51ad002e39c5" xlink:to="loc_us-gaap_SharePrice_019cb481-9f12-7033-b1c6-e2e0d1d03768" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_019cb481-9f12-7ff7-b889-56a5707f5a90" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentConvertibleConversionPrice1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueBalanceSheetGroupingFinancialStatementCaptionsLineItems_019cb481-9f12-7a9f-b9f1-51ad002e39c5" xlink:to="loc_us-gaap_DebtInstrumentConvertibleConversionPrice1_019cb481-9f12-7ff7-b889-56a5707f5a90" xlink:type="arc" order="5"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/FINANCIALINSTRUMENTSScheduleofInvestmentsWithoutReadilyDeterminableFairValueDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#FINANCIALINSTRUMENTSScheduleofInvestmentsWithoutReadilyDeterminableFairValueDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/FINANCIALINSTRUMENTSScheduleofInvestmentsWithoutReadilyDeterminableFairValueDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019cb481-9f12-78ea-a0d3-53cf5e681332" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019cb481-9f12-79c7-91dd-09f6a5de131f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019cb481-9f12-78ea-a0d3-53cf5e681332" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019cb481-9f12-79c7-91dd-09f6a5de131f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019cb481-9f12-769b-ab9a-b7892501e531" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019cb481-9f12-79c7-91dd-09f6a5de131f" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019cb481-9f12-769b-ab9a-b7892501e531" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-769b-ab9a-b7892501e531_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019cb481-9f12-769b-ab9a-b7892501e531" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-769b-ab9a-b7892501e531_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-7a36-a563-3586ccc0c91c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019cb481-9f12-769b-ab9a-b7892501e531" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-7a36-a563-3586ccc0c91c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquitySecuritiesMember_019cb481-9f12-7d8c-a183-bd44e5858d0b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquitySecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-7a36-a563-3586ccc0c91c" xlink:to="loc_us-gaap_EquitySecuritiesMember_019cb481-9f12-7d8c-a183-bd44e5858d0b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ConvertibleNotesReceivableMember_019cb481-9f12-7d82-b0ac-74e5c715de68" xlink:href="pcrx-20260331.xsd#pcrx_ConvertibleNotesReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-7a36-a563-3586ccc0c91c" xlink:to="loc_pcrx_ConvertibleNotesReceivableMember_019cb481-9f12-7d82-b0ac-74e5c715de68" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_019cb481-9f12-7752-8cc5-29cdf032a481" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019cb481-9f12-79c7-91dd-09f6a5de131f" xlink:to="loc_srt_OwnershipAxis_019cb481-9f12-7752-8cc5-29cdf032a481" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019cb481-9f12-7752-8cc5-29cdf032a481_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_019cb481-9f12-7752-8cc5-29cdf032a481" xlink:to="loc_srt_OwnershipDomain_019cb481-9f12-7752-8cc5-29cdf032a481_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019cb481-9f12-7c69-b5a6-d385a8930fd2" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_019cb481-9f12-7752-8cc5-29cdf032a481" xlink:to="loc_srt_OwnershipDomain_019cb481-9f12-7c69-b5a6-d385a8930fd2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_GQBioAcquisitionMember_019cb481-9f12-7747-8bce-3b11cc6285fb" xlink:href="pcrx-20260331.xsd#pcrx_GQBioAcquisitionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019cb481-9f12-7c69-b5a6-d385a8930fd2" xlink:to="loc_pcrx_GQBioAcquisitionMember_019cb481-9f12-7747-8bce-3b11cc6285fb" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019cb481-9f12-7475-a881-cf53229c2a3b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019cb481-9f12-79c7-91dd-09f6a5de131f" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019cb481-9f12-7475-a881-cf53229c2a3b" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cb481-9f12-7475-a881-cf53229c2a3b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019cb481-9f12-7475-a881-cf53229c2a3b" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cb481-9f12-7475-a881-cf53229c2a3b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cb481-9f12-74da-b5e9-290607ec4025" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019cb481-9f12-7475-a881-cf53229c2a3b" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cb481-9f12-74da-b5e9-290607ec4025" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_GQBioAcquisitionMember_019cb481-9f12-7315-b600-e1ddae9a1b10" xlink:href="pcrx-20260331.xsd#pcrx_GQBioAcquisitionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cb481-9f12-74da-b5e9-290607ec4025" xlink:to="loc_pcrx_GQBioAcquisitionMember_019cb481-9f12-7315-b600-e1ddae9a1b10" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019cb481-9f12-7e5f-bda7-47f65a3a05a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019cb481-9f12-78ea-a0d3-53cf5e681332" xlink:to="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019cb481-9f12-7e5f-bda7-47f65a3a05a0" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_019cb481-9f12-762a-9cb4-02344c83668f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019cb481-9f12-7e5f-bda7-47f65a3a05a0" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_019cb481-9f12-762a-9cb4-02344c83668f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_019cb481-9f12-795e-8954-3f5506fe77c7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019cb481-9f12-7e5f-bda7-47f65a3a05a0" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPurchases_019cb481-9f12-795e-8954-3f5506fe77c7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetImpairments_019cb481-9f12-7d6f-bfd1-1f92c0c8389d" xlink:href="pcrx-20260331.xsd#pcrx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetImpairments"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019cb481-9f12-7e5f-bda7-47f65a3a05a0" xlink:to="loc_pcrx_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetImpairments_019cb481-9f12-7d6f-bfd1-1f92c0c8389d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_019cb481-9f12-7b73-bbe1-93ce79dffe49" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019cb481-9f12-7e5f-bda7-47f65a3a05a0" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetGainLossIncludedInEarnings1_019cb481-9f12-7b73-bbe1-93ce79dffe49" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements_019cb481-9f12-75d5-a077-a823fdd773a0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019cb481-9f12-7e5f-bda7-47f65a3a05a0" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetSettlements_019cb481-9f12-75d5-a077-a823fdd773a0" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019cb481-9f12-7fe0-b7de-0df744be7b94" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019cb481-9f12-7e5f-bda7-47f65a3a05a0" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019cb481-9f12-7fe0-b7de-0df744be7b94" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease_019d4473-2966-7429-9008-18860428e64e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019cb481-9f12-7e5f-bda7-47f65a3a05a0" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetPeriodIncreaseDecrease_019d4473-2966-7429-9008-18860428e64e" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue_019cb481-9f12-799a-be06-9c07883c7b25" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisAssetValue"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019cb481-9f12-75c1-a00a-b9287cbd3c7b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019cb481-9f12-78ea-a0d3-53cf5e681332" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019cb481-9f12-75c1-a00a-b9287cbd3c7b" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/FINANCIALINSTRUMENTSNarrativeDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#FINANCIALINSTRUMENTSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/FINANCIALINSTRUMENTSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9f12-7116-95c3-bd9ac5076c6c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTable_019cb481-9f12-7cdf-8134-8b37fe6ab029" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9f12-7116-95c3-bd9ac5076c6c" xlink:to="loc_us-gaap_ConcentrationRiskTable_019cb481-9f12-7cdf-8134-8b37fe6ab029" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019d1ff8-22bd-797e-8792-6b4f886bf6d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019cb481-9f12-7cdf-8134-8b37fe6ab029" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019d1ff8-22bd-797e-8792-6b4f886bf6d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d1ff8-22bd-797e-8792-6b4f886bf6d3_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d1ff8-22bd-797e-8792-6b4f886bf6d3" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d1ff8-22bd-797e-8792-6b4f886bf6d3_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d1ff8-22bd-7e29-a219-09c1cdce2d32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019d1ff8-22bd-797e-8792-6b4f886bf6d3" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d1ff8-22bd-7e29-a219-09c1cdce2d32" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_EquityInvestmentAndConvertibleNoteReceivableMember_019d1ff8-22bd-78b6-941f-8b9e49b7199d" xlink:href="pcrx-20260331.xsd#pcrx_EquityInvestmentAndConvertibleNoteReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d1ff8-22bd-7e29-a219-09c1cdce2d32" xlink:to="loc_pcrx_EquityInvestmentAndConvertibleNoteReceivableMember_019d1ff8-22bd-78b6-941f-8b9e49b7199d" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ContingentConsiderationMember_019d1ff8-5c08-7524-beb5-e25abe760b73" xlink:href="pcrx-20260331.xsd#pcrx_ContingentConsiderationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019d1ff8-22bd-7e29-a219-09c1cdce2d32" xlink:to="loc_pcrx_ContingentConsiderationMember_019d1ff8-5c08-7524-beb5-e25abe760b73" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_019d1ff8-22bd-7636-bad9-556ab8da8d0f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019cb481-9f12-7cdf-8134-8b37fe6ab029" xlink:to="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_019d1ff8-22bd-7636-bad9-556ab8da8d0f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_019d1ff8-22bd-7636-bad9-556ab8da8d0f_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_019d1ff8-22bd-7636-bad9-556ab8da8d0f" xlink:to="loc_us-gaap_ReceivableTypeDomain_019d1ff8-22bd-7636-bad9-556ab8da8d0f_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReceivableTypeDomain_019d1ff8-22bd-75d1-99e4-c275f85150dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReceivableTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis_019d1ff8-22bd-7636-bad9-556ab8da8d0f" xlink:to="loc_us-gaap_ReceivableTypeDomain_019d1ff8-22bd-75d1-99e4-c275f85150dd" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ConvertibleNoteReceivableMember_019d1ff8-22bd-7664-97fa-2bd7b396a411" xlink:href="pcrx-20260331.xsd#pcrx_ConvertibleNoteReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ReceivableTypeDomain_019d1ff8-22bd-75d1-99e4-c275f85150dd" xlink:to="loc_pcrx_ConvertibleNoteReceivableMember_019d1ff8-22bd-7664-97fa-2bd7b396a411" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019d1ff8-22bd-7139-b34a-8ab66e00daa8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019cb481-9f12-7cdf-8134-8b37fe6ab029" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019d1ff8-22bd-7139-b34a-8ab66e00daa8" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d1ff8-22bd-7139-b34a-8ab66e00daa8_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019d1ff8-22bd-7139-b34a-8ab66e00daa8" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d1ff8-22bd-7139-b34a-8ab66e00daa8_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d1ff8-22bd-7034-97dd-44299aa82806" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019d1ff8-22bd-7139-b34a-8ab66e00daa8" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d1ff8-22bd-7034-97dd-44299aa82806" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_FlexionAcquisitionMember_019d1ff8-22bd-7c28-896d-0a4e67c5afa6" xlink:href="pcrx-20260331.xsd#pcrx_FlexionAcquisitionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019d1ff8-22bd-7034-97dd-44299aa82806" xlink:to="loc_pcrx_FlexionAcquisitionMember_019d1ff8-22bd-7c28-896d-0a4e67c5afa6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019d1ff8-5c08-7356-a3a1-a910a779f606" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019cb481-9f12-7cdf-8134-8b37fe6ab029" xlink:to="loc_srt_RangeAxis_019d1ff8-5c08-7356-a3a1-a910a779f606" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d1ff8-5c08-7356-a3a1-a910a779f606_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019d1ff8-5c08-7356-a3a1-a910a779f606" xlink:to="loc_srt_RangeMember_019d1ff8-5c08-7356-a3a1-a910a779f606_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019d1ff8-5c08-7547-a099-513d50f8c220" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019d1ff8-5c08-7356-a3a1-a910a779f606" xlink:to="loc_srt_RangeMember_019d1ff8-5c08-7547-a099-513d50f8c220" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_WeightedAverageMember_019d1ff8-5c08-7e1a-ac2d-2686038b2cb9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_WeightedAverageMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019d1ff8-5c08-7547-a099-513d50f8c220" xlink:to="loc_srt_WeightedAverageMember_019d1ff8-5c08-7e1a-ac2d-2686038b2cb9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d1ff8-5c08-74b8-a311-9d254b45989d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019cb481-9f12-7cdf-8134-8b37fe6ab029" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d1ff8-5c08-74b8-a311-9d254b45989d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d1ff8-5c08-74b8-a311-9d254b45989d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d1ff8-5c08-74b8-a311-9d254b45989d" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d1ff8-5c08-74b8-a311-9d254b45989d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d1ff8-5c08-729e-8d68-2fa8bc59e471" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019d1ff8-5c08-74b8-a311-9d254b45989d" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d1ff8-5c08-729e-8d68-2fa8bc59e471" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019d1ff8-5c08-7e0b-bc68-d7ddef2b4200" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019d1ff8-5c08-729e-8d68-2fa8bc59e471" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019d1ff8-5c08-7e0b-bc68-d7ddef2b4200" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019d1ff8-5c08-7fbf-8246-d3be6ad85cfb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019cb481-9f12-7cdf-8134-8b37fe6ab029" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019d1ff8-5c08-7fbf-8246-d3be6ad85cfb" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019d1ff8-5c08-7fbf-8246-d3be6ad85cfb_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019d1ff8-5c08-7fbf-8246-d3be6ad85cfb" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019d1ff8-5c08-7fbf-8246-d3be6ad85cfb_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019d1ff8-5c08-7b34-a41e-574f14ca81e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019d1ff8-5c08-7fbf-8246-d3be6ad85cfb" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019d1ff8-5c08-7b34-a41e-574f14ca81e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_019d1ff8-5c08-7911-b99b-d77bd5641fc3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019d1ff8-5c08-7b34-a41e-574f14ca81e7" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_019d1ff8-5c08-7911-b99b-d77bd5641fc3" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MajorCustomersAxis_019d1ff8-a802-7782-9c89-b89ba979caf9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MajorCustomersAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019cb481-9f12-7cdf-8134-8b37fe6ab029" xlink:to="loc_srt_MajorCustomersAxis_019d1ff8-a802-7782-9c89-b89ba979caf9" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019d1ff8-a802-7782-9c89-b89ba979caf9_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_MajorCustomersAxis_019d1ff8-a802-7782-9c89-b89ba979caf9" xlink:to="loc_srt_NameOfMajorCustomerDomain_019d1ff8-a802-7782-9c89-b89ba979caf9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_NameOfMajorCustomerDomain_019d1ff8-a802-774b-b70e-89652b9c64ea" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_NameOfMajorCustomerDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_MajorCustomersAxis_019d1ff8-a802-7782-9c89-b89ba979caf9" xlink:to="loc_srt_NameOfMajorCustomerDomain_019d1ff8-a802-774b-b70e-89652b9c64ea" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_MajorCustomerOneMember_019d1ff8-a802-73b7-8c3f-32d4b0887323" xlink:href="pcrx-20260331.xsd#pcrx_MajorCustomerOneMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019d1ff8-a802-774b-b70e-89652b9c64ea" xlink:to="loc_pcrx_MajorCustomerOneMember_019d1ff8-a802-73b7-8c3f-32d4b0887323" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_MajorCustomerTwoMember_019d1ff8-a802-73ca-8d45-ba517b2a522f" xlink:href="pcrx-20260331.xsd#pcrx_MajorCustomerTwoMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019d1ff8-a802-774b-b70e-89652b9c64ea" xlink:to="loc_pcrx_MajorCustomerTwoMember_019d1ff8-a802-73ca-8d45-ba517b2a522f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_MajorCustomerThreeMember_019d1ff8-a802-7056-9723-2d6e5b0a1dec" xlink:href="pcrx-20260331.xsd#pcrx_MajorCustomerThreeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019d1ff8-a802-774b-b70e-89652b9c64ea" xlink:to="loc_pcrx_MajorCustomerThreeMember_019d1ff8-a802-7056-9723-2d6e5b0a1dec" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_IoveraMember_019d1ff8-a802-705d-bea2-ce3d5fb2d7a4" xlink:href="pcrx-20260331.xsd#pcrx_IoveraMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_NameOfMajorCustomerDomain_019d1ff8-a802-774b-b70e-89652b9c64ea" xlink:to="loc_pcrx_IoveraMember_019d1ff8-a802-705d-bea2-ce3d5fb2d7a4" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1ff8-a802-76bb-9a64-59c32d4e4a36" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019cb481-9f12-7cdf-8134-8b37fe6ab029" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1ff8-a802-76bb-9a64-59c32d4e4a36" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1ff8-a802-76bb-9a64-59c32d4e4a36_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1ff8-a802-76bb-9a64-59c32d4e4a36" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1ff8-a802-76bb-9a64-59c32d4e4a36_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1ff8-a802-76b3-9bde-ded06c0b573f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019d1ff8-a802-76bb-9a64-59c32d4e4a36" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1ff8-a802-76b3-9bde-ded06c0b573f" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccountsReceivableMember_019d1ff8-a802-7573-9031-4811cc17e791" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccountsReceivableMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019d1ff8-a802-76b3-9bde-ded06c0b573f" xlink:to="loc_us-gaap_AccountsReceivableMember_019d1ff8-a802-7573-9031-4811cc17e791" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1ff8-a802-7585-8775-13c0f97a7ae7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ConcentrationRiskTable_019cb481-9f12-7cdf-8134-8b37fe6ab029" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1ff8-a802-7585-8775-13c0f97a7ae7" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019d1ff8-a802-7585-8775-13c0f97a7ae7_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1ff8-a802-7585-8775-13c0f97a7ae7" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019d1ff8-a802-7585-8775-13c0f97a7ae7_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019d1ff8-a802-7fb7-bbfc-c7e85ec849e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019d1ff8-a802-7585-8775-13c0f97a7ae7" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019d1ff8-a802-7fb7-bbfc-c7e85ec849e7" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CustomerConcentrationRiskMember_019d1ff8-a802-75ff-8486-70a141faa1c4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CustomerConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019d1ff8-a802-7fb7-bbfc-c7e85ec849e7" xlink:to="loc_us-gaap_CustomerConcentrationRiskMember_019d1ff8-a802-75ff-8486-70a141faa1c4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AssetImpairmentCharges_019d1ff8-22bd-7296-a01e-233d702b9456" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AssetImpairmentCharges"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9f12-7116-95c3-bd9ac5076c6c" xlink:to="loc_us-gaap_AssetImpairmentCharges_019d1ff8-22bd-7296-a01e-233d702b9456" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PaymentsToAcquireNotesReceivable_019d1ff8-22bd-72a8-83af-2a6a1d6a805e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PaymentsToAcquireNotesReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9f12-7116-95c3-bd9ac5076c6c" xlink:to="loc_us-gaap_PaymentsToAcquireNotesReceivable_019d1ff8-22bd-72a8-83af-2a6a1d6a805e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019d1ff8-22bd-710c-b7a5-6ddc6bf011c5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9f12-7116-95c3-bd9ac5076c6c" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiability_019d1ff8-22bd-710c-b7a5-6ddc6bf011c5" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ContingentConsiderationPaymentTerm_019d1ff8-5c08-75aa-983b-2d3236ec20e0" xlink:href="pcrx-20260331.xsd#pcrx_ContingentConsiderationPaymentTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9f12-7116-95c3-bd9ac5076c6c" xlink:to="loc_pcrx_ContingentConsiderationPaymentTerm_019d1ff8-5c08-75aa-983b-2d3236ec20e0" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_019d1ff8-5c08-7a3d-8448-73afdb8f4861" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9f12-7116-95c3-bd9ac5076c6c" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_019d1ff8-5c08-7a3d-8448-73afdb8f4861" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput_019d1ff8-5c08-7c66-8213-fa65ceff7841" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9f12-7116-95c3-bd9ac5076c6c" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput_019d1ff8-5c08-7c66-8213-fa65ceff7841" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_InterestReceivable_019d1ff8-a802-7bf4-94ad-2c7ee8caef83" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_InterestReceivable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9f12-7116-95c3-bd9ac5076c6c" xlink:to="loc_us-gaap_InterestReceivable_019d1ff8-a802-7bf4-94ad-2c7ee8caef83" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_NumberOfMajorCustomers_019d1ff8-a802-7df8-929c-3d22482aa128" xlink:href="pcrx-20260331.xsd#pcrx_NumberOfMajorCustomers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9f12-7116-95c3-bd9ac5076c6c" xlink:to="loc_pcrx_NumberOfMajorCustomers_019d1ff8-a802-7df8-929c-3d22482aa128" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019d1ff8-a802-788f-8b46-63e81da39c80" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9f12-7116-95c3-bd9ac5076c6c" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019d1ff8-a802-788f-8b46-63e81da39c80" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019d1ff8-a802-7e13-bee5-c5d1d53db2df" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskLineItems_019cb481-9f12-7116-95c3-bd9ac5076c6c" xlink:to="loc_us-gaap_AllowanceForDoubtfulAccountsReceivableCurrent_019d1ff8-a802-7e13-bee5-c5d1d53db2df" xlink:type="arc" order="9"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/FINANCIALINSTRUMENTSScheduleofKeyAssumptionsusedintheValuationofContingentConsiderationDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#FINANCIALINSTRUMENTSScheduleofKeyAssumptionsusedintheValuationofContingentConsiderationDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/FINANCIALINSTRUMENTSScheduleofKeyAssumptionsusedintheValuationofContingentConsiderationDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019cb481-9f12-7e94-b665-be282e8e102c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019cb481-9f12-703c-80e3-234d34b65498" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019cb481-9f12-7e94-b665-be282e8e102c" xlink:to="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019cb481-9f12-703c-80e3-234d34b65498" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cb481-9f12-76f3-80c5-6f1cb9c9947b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019cb481-9f12-703c-80e3-234d34b65498" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cb481-9f12-76f3-80c5-6f1cb9c9947b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-76f3-80c5-6f1cb9c9947b_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cb481-9f12-76f3-80c5-6f1cb9c9947b" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-76f3-80c5-6f1cb9c9947b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-74ab-ae31-96724958e3e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cb481-9f12-76f3-80c5-6f1cb9c9947b" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-74ab-ae31-96724958e3e0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel3Member_019cb481-9f12-734c-aefd-5dc6385b1bba" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel3Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-74ab-ae31-96724958e3e0" xlink:to="loc_us-gaap_FairValueInputsLevel3Member_019cb481-9f12-734c-aefd-5dc6385b1bba" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019cb481-9f12-7e44-a93e-7e6e249a2280" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019cb481-9f12-703c-80e3-234d34b65498" xlink:to="loc_srt_RangeAxis_019cb481-9f12-7e44-a93e-7e6e249a2280" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019cb481-9f12-7e44-a93e-7e6e249a2280_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019cb481-9f12-7e44-a93e-7e6e249a2280" xlink:to="loc_srt_RangeMember_019cb481-9f12-7e44-a93e-7e6e249a2280_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019cb481-9f12-73e8-af4d-f7b53b47e3cc" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019cb481-9f12-7e44-a93e-7e6e249a2280" xlink:to="loc_srt_RangeMember_019cb481-9f12-73e8-af4d-f7b53b47e3cc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019cb481-9f12-7a01-ae2f-a97a21cbc544" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019cb481-9f12-73e8-af4d-f7b53b47e3cc" xlink:to="loc_srt_MinimumMember_019cb481-9f12-7a01-ae2f-a97a21cbc544" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019cb481-9f12-759a-a38c-d1dcad1024a1" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019cb481-9f12-73e8-af4d-f7b53b47e3cc" xlink:to="loc_srt_MaximumMember_019cb481-9f12-759a-a38c-d1dcad1024a1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019cb481-9f12-7b24-b585-94026d95bbf1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019cb481-9f12-703c-80e3-234d34b65498" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019cb481-9f12-7b24-b585-94026d95bbf1" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cb481-9f12-7b24-b585-94026d95bbf1_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019cb481-9f12-7b24-b585-94026d95bbf1" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cb481-9f12-7b24-b585-94026d95bbf1_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cb481-9f12-75c0-9823-2d9b574ab74c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019cb481-9f12-7b24-b585-94026d95bbf1" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cb481-9f12-75c0-9823-2d9b574ab74c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_FlexionAcquisitionMember_019cb481-9f12-7191-9292-f68a49feb77c" xlink:href="pcrx-20260331.xsd#pcrx_FlexionAcquisitionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019cb481-9f12-75c0-9823-2d9b574ab74c" xlink:to="loc_pcrx_FlexionAcquisitionMember_019cb481-9f12-7191-9292-f68a49feb77c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019cb481-9f12-77a9-8fe3-11ee7b281264" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019cb481-9f12-703c-80e3-234d34b65498" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019cb481-9f12-77a9-8fe3-11ee7b281264" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-77a9-8fe3-11ee7b281264_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019cb481-9f12-77a9-8fe3-11ee7b281264" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-77a9-8fe3-11ee7b281264_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-790f-a666-1f340ab20834" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019cb481-9f12-77a9-8fe3-11ee7b281264" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-790f-a666-1f340ab20834" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ContingentConsiderationMember_019cb481-9f12-7c28-a608-3cbb55a4aa3b" xlink:href="pcrx-20260331.xsd#pcrx_ContingentConsiderationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-790f-a666-1f340ab20834" xlink:to="loc_pcrx_ContingentConsiderationMember_019cb481-9f12-7c28-a608-3cbb55a4aa3b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeAxis_019cb481-9f12-7fa4-915b-05710ae22d73" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesTable_019cb481-9f12-703c-80e3-234d34b65498" xlink:to="loc_us-gaap_MeasurementInputTypeAxis_019cb481-9f12-7fa4-915b-05710ae22d73" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019cb481-9f12-7fa4-915b-05710ae22d73_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019cb481-9f12-7fa4-915b-05710ae22d73" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019cb481-9f12-7fa4-915b-05710ae22d73_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputTypeDomain_019cb481-9f12-7389-8f17-0d39b4a58e88" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_MeasurementInputTypeAxis_019cb481-9f12-7fa4-915b-05710ae22d73" xlink:to="loc_us-gaap_MeasurementInputTypeDomain_019cb481-9f12-7389-8f17-0d39b4a58e88" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_MeasurementInputDiscountRateMember_019cb481-9f12-7a97-88c3-c32f70fa1e69" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_MeasurementInputDiscountRateMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019cb481-9f12-7389-8f17-0d39b4a58e88" xlink:to="loc_us-gaap_MeasurementInputDiscountRateMember_019cb481-9f12-7a97-88c3-c32f70fa1e69" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_MeasurementInputExpectedMilestonePaymentMember_019cb481-9f12-73bf-98dd-6205059c1690" xlink:href="pcrx-20260331.xsd#pcrx_MeasurementInputExpectedMilestonePaymentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_MeasurementInputTypeDomain_019cb481-9f12-7389-8f17-0d39b4a58e88" xlink:to="loc_pcrx_MeasurementInputExpectedMilestonePaymentMember_019cb481-9f12-73bf-98dd-6205059c1690" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput_019cb481-9f12-78e7-be70-7b00be8fc08f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisValuationTechniquesLineItems_019cb481-9f12-7e94-b665-be282e8e102c" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationLiabilityMeasurementInput_019cb481-9f12-78e7-be70-7b00be8fc08f" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/FINANCIALINSTRUMENTSScheduleofChangeinContingentConsiderationRecordedatFairValueUsingLevel3MeasurementsDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#FINANCIALINSTRUMENTSScheduleofChangeinContingentConsiderationRecordedatFairValueUsingLevel3MeasurementsDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/FINANCIALINSTRUMENTSScheduleofChangeinContingentConsiderationRecordedatFairValueUsingLevel3MeasurementsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019cb481-9f12-70fa-b07e-e91889fedb83" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019cb481-9f12-769d-ac4e-9c9526a56472" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019cb481-9f12-70fa-b07e-e91889fedb83" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019cb481-9f12-769d-ac4e-9c9526a56472" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByLiabilityClassAxis_019cb481-9f12-72ff-a762-1924479bec62" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByLiabilityClassAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationTable_019cb481-9f12-769d-ac4e-9c9526a56472" xlink:to="loc_us-gaap_FairValueByLiabilityClassAxis_019cb481-9f12-72ff-a762-1924479bec62" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019cb481-9f12-72ff-a762-1924479bec62_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019cb481-9f12-72ff-a762-1924479bec62" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019cb481-9f12-72ff-a762-1924479bec62_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019cb481-9f12-754a-806f-31ba19c52459" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByLiabilityClassAxis_019cb481-9f12-72ff-a762-1924479bec62" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019cb481-9f12-754a-806f-31ba19c52459" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ContingentConsiderationMember_019cb481-9f12-7cb9-bc78-e635a2208240" xlink:href="pcrx-20260331.xsd#pcrx_ContingentConsiderationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationByLiabilityClassDomain_019cb481-9f12-754a-806f-31ba19c52459" xlink:to="loc_pcrx_ContingentConsiderationMember_019cb481-9f12-7cb9-bc78-e635a2208240" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019cb481-9f12-7f88-b0f6-a4859b347e02" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationLineItems_019cb481-9f12-70fa-b07e-e91889fedb83" xlink:to="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019cb481-9f12-7f88-b0f6-a4859b347e02" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019cb481-9f12-7be2-a752-223edbd8a934" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019cb481-9f12-7f88-b0f6-a4859b347e02" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019cb481-9f12-7be2-a752-223edbd8a934" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019cb481-9f12-7ac5-b6b8-6584e7f970e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueLiabilitiesMeasuredOnRecurringBasisUnobservableInputReconciliationCalculationRollForward_019cb481-9f12-7f88-b0f6-a4859b347e02" xlink:to="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationRecurringBasisLiabilityGainLossIncludedInEarnings_019cb481-9f12-7ac5-b6b8-6584e7f970e7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue_019cb481-9f12-7cea-9035-ec6599877521" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementWithUnobservableInputsReconciliationsRecurringBasisLiabilityValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/FINANCIALINSTRUMENTSScheduleofShortTermandNoncurrentAvailableforSaleInvestmentsDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#FINANCIALINSTRUMENTSScheduleofShortTermandNoncurrentAvailableforSaleInvestmentsDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/FINANCIALINSTRUMENTSScheduleofShortTermandNoncurrentAvailableforSaleInvestmentsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019cb481-9f12-7388-b55f-2023d95d78d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ScheduleOfShortTermAndNoncurrentAvailableForSaleInvestmentsTable_019cb481-9f12-7c99-8328-494b4c8225e9" xlink:href="pcrx-20260331.xsd#pcrx_ScheduleOfShortTermAndNoncurrentAvailableForSaleInvestmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019cb481-9f12-7388-b55f-2023d95d78d6" xlink:to="loc_pcrx_ScheduleOfShortTermAndNoncurrentAvailableForSaleInvestmentsTable_019cb481-9f12-7c99-8328-494b4c8225e9" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FinancialInstrumentAxis_019cb481-9f12-7809-ab79-7cc287acb5ed" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FinancialInstrumentAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pcrx_ScheduleOfShortTermAndNoncurrentAvailableForSaleInvestmentsTable_019cb481-9f12-7c99-8328-494b4c8225e9" xlink:to="loc_us-gaap_FinancialInstrumentAxis_019cb481-9f12-7809-ab79-7cc287acb5ed" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-7809-ab79-7cc287acb5ed_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019cb481-9f12-7809-ab79-7cc287acb5ed" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-7809-ab79-7cc287acb5ed_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-7b5d-804b-f22a4cceb1a2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FinancialInstrumentAxis_019cb481-9f12-7809-ab79-7cc287acb5ed" xlink:to="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-7b5d-804b-f22a4cceb1a2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CommercialPaperMember_019cb481-9f12-7ed8-808d-08504d25d726" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CommercialPaperMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-7b5d-804b-f22a4cceb1a2" xlink:to="loc_us-gaap_CommercialPaperMember_019cb481-9f12-7ed8-808d-08504d25d726" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CorporateBondSecuritiesMember_019cb481-9f12-7df5-bde0-32fc8b07761e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CorporateBondSecuritiesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_TransfersAndServicingOfFinancialInstrumentsTypesOfFinancialInstrumentsDomain_019cb481-9f12-7b5d-804b-f22a4cceb1a2" xlink:to="loc_us-gaap_CorporateBondSecuritiesMember_019cb481-9f12-7df5-bde0-32fc8b07761e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_InvestmentCategorizationAxis_019cb481-9f12-743d-9c5e-b0c72a96bea6" xlink:href="pcrx-20260331.xsd#pcrx_InvestmentCategorizationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pcrx_ScheduleOfShortTermAndNoncurrentAvailableForSaleInvestmentsTable_019cb481-9f12-7c99-8328-494b4c8225e9" xlink:to="loc_pcrx_InvestmentCategorizationAxis_019cb481-9f12-743d-9c5e-b0c72a96bea6" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_InvestmentCategorizationDomain_019cb481-9f12-743d-9c5e-b0c72a96bea6_default" xlink:href="pcrx-20260331.xsd#pcrx_InvestmentCategorizationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pcrx_InvestmentCategorizationAxis_019cb481-9f12-743d-9c5e-b0c72a96bea6" xlink:to="loc_pcrx_InvestmentCategorizationDomain_019cb481-9f12-743d-9c5e-b0c72a96bea6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_InvestmentCategorizationDomain_019cb481-9f12-773b-b063-8ea551e114ff" xlink:href="pcrx-20260331.xsd#pcrx_InvestmentCategorizationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pcrx_InvestmentCategorizationAxis_019cb481-9f12-743d-9c5e-b0c72a96bea6" xlink:to="loc_pcrx_InvestmentCategorizationDomain_019cb481-9f12-773b-b063-8ea551e114ff" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShortTermInvestmentsMember_019cb481-9f12-7364-8363-67eacb403327" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShortTermInvestmentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pcrx_InvestmentCategorizationDomain_019cb481-9f12-773b-b063-8ea551e114ff" xlink:to="loc_us-gaap_ShortTermInvestmentsMember_019cb481-9f12-7364-8363-67eacb403327" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cb481-9f12-75af-b7f4-6de609888c82" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueByFairValueHierarchyLevelAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_pcrx_ScheduleOfShortTermAndNoncurrentAvailableForSaleInvestmentsTable_019cb481-9f12-7c99-8328-494b4c8225e9" xlink:to="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cb481-9f12-75af-b7f4-6de609888c82" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-75af-b7f4-6de609888c82_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cb481-9f12-75af-b7f4-6de609888c82" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-75af-b7f4-6de609888c82_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-732d-a748-f899ac3ff2d3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueMeasurementsFairValueHierarchyDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_FairValueByFairValueHierarchyLevelAxis_019cb481-9f12-75af-b7f4-6de609888c82" xlink:to="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-732d-a748-f899ac3ff2d3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_FairValueInputsLevel2Member_019cb481-9f12-7061-8b5c-11d5ac7818e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_FairValueInputsLevel2Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_FairValueMeasurementsFairValueHierarchyDomain_019cb481-9f12-732d-a748-f899ac3ff2d3" xlink:to="loc_us-gaap_FairValueInputsLevel2Member_019cb481-9f12-7061-8b5c-11d5ac7818e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019cb481-9f12-7dca-b9e1-864e8128889a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019cb481-9f12-7388-b55f-2023d95d78d6" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis_019cb481-9f12-7dca-b9e1-864e8128889a" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019cb481-9f12-77b8-959e-fd7a7168bdd3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019cb481-9f12-7388-b55f-2023d95d78d6" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedGainBeforeTax_019cb481-9f12-77b8-959e-fd7a7168bdd3" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019cb481-9f12-7679-bdaa-3c4bbd434fc3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019cb481-9f12-7388-b55f-2023d95d78d6" xlink:to="loc_us-gaap_AvailableForSaleDebtSecuritiesAccumulatedGrossUnrealizedLossBeforeTax_019cb481-9f12-7679-bdaa-3c4bbd434fc3" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019cb481-9f12-762a-bd42-ff14748d852b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AvailableForSaleSecuritiesDebtSecurities"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ScheduleOfAvailableForSaleSecuritiesLineItems_019cb481-9f12-7388-b55f-2023d95d78d6" xlink:to="loc_us-gaap_AvailableForSaleSecuritiesDebtSecurities_019cb481-9f12-762a-bd42-ff14748d852b" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/STOCKHOLDERSEQUITYScheduleofAccumulatedOtherComprehensiveLossDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#STOCKHOLDERSEQUITYScheduleofAccumulatedOtherComprehensiveLossDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/STOCKHOLDERSEQUITYScheduleofAccumulatedOtherComprehensiveLossDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019cb481-9f12-728a-b156-3d4feccc34eb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019cb481-9f12-725c-a30f-237b7e38882d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeLossTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019cb481-9f12-728a-b156-3d4feccc34eb" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019cb481-9f12-725c-a30f-237b7e38882d" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementEquityComponentsAxis_019cb481-9f12-734d-bd40-35b27cab67dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementEquityComponentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossTable_019cb481-9f12-725c-a30f-237b7e38882d" xlink:to="loc_us-gaap_StatementEquityComponentsAxis_019cb481-9f12-734d-bd40-35b27cab67dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019cb481-9f12-734d-bd40-35b27cab67dc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019cb481-9f12-734d-bd40-35b27cab67dc" xlink:to="loc_us-gaap_EquityComponentDomain_019cb481-9f12-734d-bd40-35b27cab67dc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EquityComponentDomain_019cb481-9f12-7bd9-9ad1-3c55e827d546" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EquityComponentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementEquityComponentsAxis_019cb481-9f12-734d-bd40-35b27cab67dc" xlink:to="loc_us-gaap_EquityComponentDomain_019cb481-9f12-7bd9-9ad1-3c55e827d546" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019cb481-9f12-7614-9511-7d4fbe03a318" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedOtherComprehensiveIncomeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EquityComponentDomain_019cb481-9f12-7bd9-9ad1-3c55e827d546" xlink:to="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019cb481-9f12-7614-9511-7d4fbe03a318" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_019cb481-9f12-7c6d-a915-c51b7fcd12f8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019cb481-9f12-7614-9511-7d4fbe03a318" xlink:to="loc_us-gaap_AccumulatedNetUnrealizedInvestmentGainLossMember_019cb481-9f12-7c6d-a915-c51b7fcd12f8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AccumulatedTranslationAdjustmentMember_019cb481-9f12-7041-9089-8404513a9775" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AccumulatedTranslationAdjustmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeMember_019cb481-9f12-7614-9511-7d4fbe03a318" xlink:to="loc_us-gaap_AccumulatedTranslationAdjustmentMember_019cb481-9f12-7041-9089-8404513a9775" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019cb481-9f12-7660-816b-308f318f169e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AOCIAttributableToParentNetOfTaxRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019cb481-9f12-728a-b156-3d4feccc34eb" xlink:to="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019cb481-9f12-7660-816b-308f318f169e" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019cb481-9f12-72cb-b3d7-dfcb1b1c82aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019cb481-9f12-7660-816b-308f318f169e" xlink:to="loc_us-gaap_StockholdersEquity_019cb481-9f12-72cb-b3d7-dfcb1b1c82aa" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_019cb481-9f12-7dc9-bc1e-347ef23a3696" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019cb481-9f12-7660-816b-308f318f169e" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodNetOfTax_019cb481-9f12-7dc9-bc1e-347ef23a3696" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_019d1ffb-e657-7e9e-bc8d-611527f2eb6e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AOCIAttributableToParentNetOfTaxRollForward_019cb481-9f12-7660-816b-308f318f169e" xlink:to="loc_us-gaap_OtherComprehensiveIncomeLossForeignCurrencyTransactionAndTranslationAdjustmentNetOfTax_019d1ffb-e657-7e9e-bc8d-611527f2eb6e" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockholdersEquity_019cb481-9f12-7040-adbc-202f2c740e54" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockholdersEquity"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax_019cb481-9f12-75ad-b447-de70870e7052" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AccumulatedOtherComprehensiveIncomeLossLineItems_019cb481-9f12-728a-b156-3d4feccc34eb" xlink:to="loc_us-gaap_OtherComprehensiveIncomeUnrealizedHoldingGainLossOnSecuritiesArisingDuringPeriodTax_019cb481-9f12-75ad-b447-de70870e7052" xlink:type="arc" order="1"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/STOCKPLANSNarrativeDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#STOCKPLANSNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/STOCKPLANSNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7fa5-8b23-9f1c8ba506e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019cb481-9f12-7668-83d0-eb8de59822e0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7fa5-8b23-9f1c8ba506e7" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019cb481-9f12-7668-83d0-eb8de59822e0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameAxis_019d2019-852c-7bb0-9d40-b4e221eacb91" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019cb481-9f12-7668-83d0-eb8de59822e0" xlink:to="loc_us-gaap_PlanNameAxis_019d2019-852c-7bb0-9d40-b4e221eacb91" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019d2019-852c-7bb0-9d40-b4e221eacb91_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_PlanNameAxis_019d2019-852c-7bb0-9d40-b4e221eacb91" xlink:to="loc_us-gaap_PlanNameDomain_019d2019-852c-7bb0-9d40-b4e221eacb91_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PlanNameDomain_019d2019-852c-75cc-920c-fa6565eb68f9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_PlanNameAxis_019d2019-852c-7bb0-9d40-b4e221eacb91" xlink:to="loc_us-gaap_PlanNameDomain_019d2019-852c-75cc-920c-fa6565eb68f9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_InducementPlan2014Member_019d2019-852c-7dd3-a083-8726a22caaf8" xlink:href="pcrx-20260331.xsd#pcrx_InducementPlan2014Member"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_PlanNameDomain_019d2019-852c-75cc-920c-fa6565eb68f9" xlink:to="loc_pcrx_InducementPlan2014Member_019d2019-852c-7dd3-a083-8726a22caaf8" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019d2019-b934-743d-876e-59f45c64c0e2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019cb481-9f12-7668-83d0-eb8de59822e0" xlink:to="loc_us-gaap_AwardTypeAxis_019d2019-b934-743d-876e-59f45c64c0e2" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d2019-b934-743d-876e-59f45c64c0e2_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019d2019-b934-743d-876e-59f45c64c0e2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d2019-b934-743d-876e-59f45c64c0e2_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d2019-b934-742b-a188-d609cf6aabc2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019d2019-b934-743d-876e-59f45c64c0e2" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d2019-b934-742b-a188-d609cf6aabc2" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019d2019-b934-7444-b155-2cda70546826" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d2019-b934-742b-a188-d609cf6aabc2" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019d2019-b934-7444-b155-2cda70546826" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_019d201a-0177-75f3-b180-5372d430b6bb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019d2019-b934-742b-a188-d609cf6aabc2" xlink:to="loc_us-gaap_EmployeeStockMember_019d201a-0177-75f3-b180-5372d430b6bb" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_019d2019-852c-7a46-8cb4-f0e6f19b8485" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7fa5-8b23-9f1c8ba506e7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized_019d2019-852c-7a46-8cb4-f0e6f19b8485" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019d2019-852c-7b61-9c8e-4e743d3ab2d1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7fa5-8b23-9f1c8ba506e7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAuthorized_019d2019-852c-7b61-9c8e-4e743d3ab2d1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019d2019-852c-7e15-929d-162092dd4fbd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7fa5-8b23-9f1c8ba506e7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant_019d2019-852c-7e15-929d-162092dd4fbd" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019d2019-b934-7903-9aea-22daa52d9ee6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7fa5-8b23-9f1c8ba506e7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019d2019-b934-7903-9aea-22daa52d9ee6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfPurchasePeriods_019d201a-0177-7f7f-b062-01823618d5bc" xlink:href="pcrx-20260331.xsd#pcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfPurchasePeriods"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7fa5-8b23-9f1c8ba506e7" xlink:to="loc_pcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfPurchasePeriods_019d201a-0177-7f7f-b062-01823618d5bc" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePeriod_019d201a-0177-79e0-a165-18c6d28739e1" xlink:href="pcrx-20260331.xsd#pcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7fa5-8b23-9f1c8ba506e7" xlink:to="loc_pcrx_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasePeriod_019d201a-0177-79e0-a165-18c6d28739e1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_019d201a-0177-7d78-867d-5d79e6764b6d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7fa5-8b23-9f1c8ba506e7" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardPurchasePriceOfCommonStockPercent_019d201a-0177-7d78-867d-5d79e6764b6d" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_019d201a-0177-70bd-bb0f-d0e77a96878f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7fa5-8b23-9f1c8ba506e7" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesEmployeeStockPurchasePlans_019d201a-0177-70bd-bb0f-d0e77a96878f" xlink:type="arc" order="7"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/STOCKPLANSScheduleofStockBasedCompensationExpensesDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#STOCKPLANSScheduleofStockBasedCompensationExpensesDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/STOCKPLANSScheduleofStockBasedCompensationExpensesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019cb481-9f12-72bc-9d4c-cc453b5d80a1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019cb481-9f12-70fc-8dc9-6bbf28660eb6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019cb481-9f12-72bc-9d4c-cc453b5d80a1" xlink:to="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019cb481-9f12-70fc-8dc9-6bbf28660eb6" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationAxis_019cb481-9f12-7b6d-bf4d-656e9f2083d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019cb481-9f12-70fc-8dc9-6bbf28660eb6" xlink:to="loc_us-gaap_IncomeStatementLocationAxis_019cb481-9f12-7b6d-bf4d-656e9f2083d4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019cb481-9f12-7b6d-bf4d-656e9f2083d4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019cb481-9f12-7b6d-bf4d-656e9f2083d4" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019cb481-9f12-7b6d-bf4d-656e9f2083d4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeStatementLocationDomain_019cb481-9f12-7324-a5ba-a872ce0e40d8" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeStatementLocationDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_IncomeStatementLocationAxis_019cb481-9f12-7b6d-bf4d-656e9f2083d4" xlink:to="loc_us-gaap_IncomeStatementLocationDomain_019cb481-9f12-7324-a5ba-a872ce0e40d8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostOfSalesMember_019cb481-9f12-775c-a04a-15f864ad5111" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostOfSalesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019cb481-9f12-7324-a5ba-a872ce0e40d8" xlink:to="loc_us-gaap_CostOfSalesMember_019cb481-9f12-775c-a04a-15f864ad5111" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ResearchAndDevelopmentExpenseMember_019cb481-9f12-7f56-af04-282e689685dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ResearchAndDevelopmentExpenseMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019cb481-9f12-7324-a5ba-a872ce0e40d8" xlink:to="loc_us-gaap_ResearchAndDevelopmentExpenseMember_019cb481-9f12-7f56-af04-282e689685dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_019cb481-9f12-795b-8e06-c5bab2b79657" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SellingGeneralAndAdministrativeExpensesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_IncomeStatementLocationDomain_019cb481-9f12-7324-a5ba-a872ce0e40d8" xlink:to="loc_us-gaap_SellingGeneralAndAdministrativeExpensesMember_019cb481-9f12-795b-8e06-c5bab2b79657" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019cb481-9f12-763c-bbcf-140484e64ccc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsTable_019cb481-9f12-70fc-8dc9-6bbf28660eb6" xlink:to="loc_us-gaap_AwardTypeAxis_019cb481-9f12-763c-bbcf-140484e64ccc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-763c-bbcf-140484e64ccc_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019cb481-9f12-763c-bbcf-140484e64ccc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-763c-bbcf-140484e64ccc_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-7aa4-8784-219e496b5410" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019cb481-9f12-763c-bbcf-140484e64ccc" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-7aa4-8784-219e496b5410" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019cb481-9f12-7132-8f8b-a226cdab1d5b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-7aa4-8784-219e496b5410" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019cb481-9f12-7132-8f8b-a226cdab1d5b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019cb481-9f12-740c-a8a7-f1ccf4862c48" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-7aa4-8784-219e496b5410" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019cb481-9f12-740c-a8a7-f1ccf4862c48" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019d2005-3b8b-7262-834c-d01855579310" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-7aa4-8784-219e496b5410" xlink:to="loc_us-gaap_PerformanceSharesMember_019d2005-3b8b-7262-834c-d01855579310" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_019cb481-9f12-7163-b23d-d89aa1549201" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-7aa4-8784-219e496b5410" xlink:to="loc_us-gaap_EmployeeStockMember_019cb481-9f12-7163-b23d-d89aa1549201" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AllocatedShareBasedCompensationExpense_019cb481-9f12-71cd-b2e9-7265912910e5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AllocatedShareBasedCompensationExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EmployeeServiceShareBasedCompensationAllocationOfRecognizedPeriodCostsLineItems_019cb481-9f12-72bc-9d4c-cc453b5d80a1" xlink:to="loc_us-gaap_AllocatedShareBasedCompensationExpense_019cb481-9f12-71cd-b2e9-7265912910e5" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/STOCKPLANSScheduleofStockBasedCompensationActivityDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#STOCKPLANSScheduleofStockBasedCompensationActivityDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/STOCKPLANSScheduleofStockBasedCompensationActivityDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-73bb-ac16-b404c36bf4aa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019cb481-9f12-7274-ac05-bb31f7baae9e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-73bb-ac16-b404c36bf4aa" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019cb481-9f12-7274-ac05-bb31f7baae9e" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019cb481-9f12-742b-8f3f-79b25c326c12" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019cb481-9f12-7274-ac05-bb31f7baae9e" xlink:to="loc_us-gaap_AwardTypeAxis_019cb481-9f12-742b-8f3f-79b25c326c12" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-742b-8f3f-79b25c326c12_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019cb481-9f12-742b-8f3f-79b25c326c12" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-742b-8f3f-79b25c326c12_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-72cb-b990-44853c04c2e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019cb481-9f12-742b-8f3f-79b25c326c12" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-72cb-b990-44853c04c2e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_RestrictedStockUnitsAndPerformanceStockUnitsMember_019d9531-f19d-7462-89f6-267545282866" xlink:href="pcrx-20260331.xsd#pcrx_RestrictedStockUnitsAndPerformanceStockUnitsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-72cb-b990-44853c04c2e4" xlink:to="loc_pcrx_RestrictedStockUnitsAndPerformanceStockUnitsMember_019d9531-f19d-7462-89f6-267545282866" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019cb481-9f12-7608-9e3f-b49cc82fa4b1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pcrx_RestrictedStockUnitsAndPerformanceStockUnitsMember_019d9531-f19d-7462-89f6-267545282866" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019cb481-9f12-7608-9e3f-b49cc82fa4b1" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PerformanceSharesMember_019d201b-71da-71f5-8022-28eb8b59ad3a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PerformanceSharesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pcrx_RestrictedStockUnitsAndPerformanceStockUnitsMember_019d9531-f19d-7462-89f6-267545282866" xlink:to="loc_us-gaap_PerformanceSharesMember_019d201b-71da-71f5-8022-28eb8b59ad3a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019cb481-9f12-705a-9971-10bb859cb8e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-73bb-ac16-b404c36bf4aa" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019cb481-9f12-705a-9971-10bb859cb8e4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019cb481-9f12-75a4-b5d9-e5b543827010" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019cb481-9f12-705a-9971-10bb859cb8e4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019cb481-9f12-75a4-b5d9-e5b543827010" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019cb481-9f12-7abc-9e3f-9dece882f45b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019cb481-9f12-705a-9971-10bb859cb8e4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodGross_019cb481-9f12-7abc-9e3f-9dece882f45b" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019cb481-9f12-709c-8015-f4de9908d158" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019cb481-9f12-705a-9971-10bb859cb8e4" xlink:to="loc_us-gaap_StockIssuedDuringPeriodSharesStockOptionsExercised_019cb481-9f12-709c-8015-f4de9908d158" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_019cb481-9f12-7af4-8382-472288c17796" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019cb481-9f12-705a-9971-10bb859cb8e4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsForfeituresInPeriod_019cb481-9f12-7af4-8382-472288c17796" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod_019cb481-9f12-782f-8897-201c098803e1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingRollForward_019cb481-9f12-705a-9971-10bb859cb8e4" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExpirationsInPeriod_019cb481-9f12-782f-8897-201c098803e1" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber_019cb481-9f12-7103-8901-65f32e2a0d5c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019cb481-9f12-72a9-a11c-f59e0e9df653" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-73bb-ac16-b404c36bf4aa" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019cb481-9f12-72a9-a11c-f59e0e9df653" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_019cb481-9f12-7532-b90d-cdf1aadc9aae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019cb481-9f12-72a9-a11c-f59e0e9df653" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_019cb481-9f12-7532-b90d-cdf1aadc9aae" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_019cb481-9f12-7030-89bc-b54eb7d4663f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019cb481-9f12-72a9-a11c-f59e0e9df653" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageExercisePrice_019cb481-9f12-7030-89bc-b54eb7d4663f" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_019cb481-9f12-75ce-83c6-3f5c8cd74282" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019cb481-9f12-72a9-a11c-f59e0e9df653" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExercisesInPeriodWeightedAverageExercisePrice_019cb481-9f12-75ce-83c6-3f5c8cd74282" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_019cb481-9f12-748d-9237-5c5726833416" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019cb481-9f12-72a9-a11c-f59e0e9df653" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsForfeituresInPeriodWeightedAverageExercisePrice_019cb481-9f12-748d-9237-5c5726833416" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice_019cb481-9f12-72c8-952d-6516f18d7e3d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePriceRollforward_019cb481-9f12-72a9-a11c-f59e0e9df653" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardOptionsExpirationsInPeriodWeightedAverageExercisePrice_019cb481-9f12-72c8-952d-6516f18d7e3d" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice_019cb481-9f12-79ed-9adf-94c820b25ea1" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019cb481-9f12-7c8c-808b-06f71af205e7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-73bb-ac16-b404c36bf4aa" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019cb481-9f12-7c8c-808b-06f71af205e7" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019cb481-9f12-7c5e-94e0-a3bb469d4acc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019cb481-9f12-7c8c-808b-06f71af205e7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019cb481-9f12-7c5e-94e0-a3bb469d4acc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019cb481-9f12-76d6-887d-17cd2df56592" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019cb481-9f12-7c8c-808b-06f71af205e7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod_019cb481-9f12-76d6-887d-17cd2df56592" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019cb481-9f12-78e7-9798-eb05839bff0f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019cb481-9f12-7c8c-808b-06f71af205e7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriod_019cb481-9f12-78e7-9798-eb05839bff0f" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019cb481-9f12-763b-a84d-77acef58931a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedRollForward_019cb481-9f12-7c8c-808b-06f71af205e7" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeitedInPeriod_019cb481-9f12-763b-a84d-77acef58931a" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber_019cb481-9f12-70dd-a328-1652583efd04" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedNumber"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019cb481-9f12-7fb3-ad20-01659096e682" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-73bb-ac16-b404c36bf4aa" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019cb481-9f12-7fb3-ad20-01659096e682" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019cb481-9f12-7b71-a9cb-d93969ee0d31" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019cb481-9f12-7fb3-ad20-01659096e682" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019cb481-9f12-7b71-a9cb-d93969ee0d31" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019cb481-9f12-76db-a721-c7511c7a07fb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019cb481-9f12-7fb3-ad20-01659096e682" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue_019cb481-9f12-76db-a721-c7511c7a07fb" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019cb481-9f12-718f-9b8f-d6759c77ba98" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019cb481-9f12-7fb3-ad20-01659096e682" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsVestedInPeriodWeightedAverageGrantDateFairValue_019cb481-9f12-718f-9b8f-d6759c77ba98" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019cb481-9f12-7e34-aa3d-e0ca0f43717e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValueRollForward_019cb481-9f12-7fb3-ad20-01659096e682" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsForfeituresWeightedAverageGrantDateFairValue_019cb481-9f12-7e34-aa3d-e0ca0f43717e" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue_019cb481-9f12-7d2a-8257-7d6e06afda3b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsNonvestedWeightedAverageGrantDateFairValue"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/STOCKPLANSScheduleofValuationAssumptionsDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#STOCKPLANSScheduleofValuationAssumptionsDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/STOCKPLANSScheduleofValuationAssumptionsDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7d59-8047-96c2e5d118dd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019cb481-9f12-71a2-9b9a-f02d8de0b7db" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7d59-8047-96c2e5d118dd" xlink:to="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019cb481-9f12-71a2-9b9a-f02d8de0b7db" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019cb481-9f12-718b-8ccd-ac521fb46578" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfShareBasedCompensationArrangementsByShareBasedPaymentAwardTable_019cb481-9f12-71a2-9b9a-f02d8de0b7db" xlink:to="loc_us-gaap_AwardTypeAxis_019cb481-9f12-718b-8ccd-ac521fb46578" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-718b-8ccd-ac521fb46578_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019cb481-9f12-718b-8ccd-ac521fb46578" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-718b-8ccd-ac521fb46578_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-7666-91c6-6905a6e41969" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019cb481-9f12-718b-8ccd-ac521fb46578" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-7666-91c6-6905a6e41969" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019cb481-9f12-7759-afef-b03ce464745c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-7666-91c6-6905a6e41969" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019cb481-9f12-7759-afef-b03ce464745c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019cb481-9f12-71a8-a6ff-7a907db9c8ae" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7d59-8047-96c2e5d118dd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate_019cb481-9f12-71a8-a6ff-7a907db9c8ae" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019cb481-9f12-7171-8b7b-c05d8674fdd5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7d59-8047-96c2e5d118dd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate_019cb481-9f12-7171-8b7b-c05d8674fdd5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019cb481-9f12-7482-bf32-e1c31dc631ea" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7d59-8047-96c2e5d118dd" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate_019cb481-9f12-7482-bf32-e1c31dc631ea" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019cb481-9f12-7def-bfd6-fba9c8afd6ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardLineItems_019cb481-9f12-7d59-8047-96c2e5d118dd" xlink:to="loc_us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardFairValueAssumptionsExpectedTerm1_019cb481-9f12-7def-bfd6-fba9c8afd6ec" xlink:type="arc" order="3"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/NETINCOMEPERCOMMONSHAREScheduleofComputationofEPSDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#NETINCOMEPERCOMMONSHAREScheduleofComputationofEPSDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/NETINCOMEPERCOMMONSHAREScheduleofComputationofEPSDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019cb481-9f12-7d17-8ef3-d9d05c8516ec" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019cb481-9f12-7457-b666-87a250663baa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019cb481-9f12-7d17-8ef3-d9d05c8516ec" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019cb481-9f12-7457-b666-87a250663baa" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AwardTypeAxis_019cb481-9f12-74f6-937d-c62fde1a340c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AwardTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019cb481-9f12-7457-b666-87a250663baa" xlink:to="loc_us-gaap_AwardTypeAxis_019cb481-9f12-74f6-937d-c62fde1a340c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-74f6-937d-c62fde1a340c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AwardTypeAxis_019cb481-9f12-74f6-937d-c62fde1a340c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-74f6-937d-c62fde1a340c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-72e8-9f47-05232bb11e1d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AwardTypeAxis_019cb481-9f12-74f6-937d-c62fde1a340c" xlink:to="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-72e8-9f47-05232bb11e1d" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019cb481-9f12-79d5-9534-027ea0901dd9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-72e8-9f47-05232bb11e1d" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019cb481-9f12-79d5-9534-027ea0901dd9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019cb481-9f12-7fd5-96f4-eeb4beb0d8f0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-72e8-9f47-05232bb11e1d" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019cb481-9f12-7fd5-96f4-eeb4beb0d8f0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_019cb481-9f12-7b5d-84ba-73f9dce5205a" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ShareBasedCompensationArrangementsByShareBasedPaymentAwardAwardTypeAndPlanNameDomain_019cb481-9f12-72e8-9f47-05232bb11e1d" xlink:to="loc_us-gaap_EmployeeStockMember_019cb481-9f12-7b5d-84ba-73f9dce5205a" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_019cb481-9f12-709b-a8e8-f1b6e240255f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019cb481-9f12-7d17-8ef3-d9d05c8516ec" xlink:to="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_019cb481-9f12-709b-a8e8-f1b6e240255f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019cb481-9f12-76cb-967e-b776a968c727" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_NetIncomeLossAvailableToCommonStockholdersBasicAbstract_019cb481-9f12-709b-a8e8-f1b6e240255f" xlink:to="loc_us-gaap_NetIncomeLoss_019cb481-9f12-76cb-967e-b776a968c727" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019cb481-9f12-706a-9e02-8b6cc2157e29" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019cb481-9f12-7d17-8ef3-d9d05c8516ec" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019cb481-9f12-706a-9e02-8b6cc2157e29" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019cb481-9f12-7109-a9ac-54be823c3454" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfSharesOutstandingBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019cb481-9f12-706a-9e02-8b6cc2157e29" xlink:to="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingBasic_019cb481-9f12-7109-a9ac-54be823c3454" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_019cb481-9f12-71fa-9e93-477707b60298" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019cb481-9f12-706a-9e02-8b6cc2157e29" xlink:to="loc_us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements_019cb481-9f12-71fa-9e93-477707b60298" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019cb481-9f12-7e09-a353-84ec38554df7" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_WeightedAverageNumberOfSharesOutstandingAbstract_019cb481-9f12-706a-9e02-8b6cc2157e29" xlink:to="loc_us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding_019cb481-9f12-7e09-a353-84ec38554df7" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_EarningsPerShareBasicAndDilutedEPSAbstract_019cb481-9f12-7ab0-80e5-b3df11f79893" xlink:href="pcrx-20260331.xsd#pcrx_EarningsPerShareBasicAndDilutedEPSAbstract"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019cb481-9f12-7d17-8ef3-d9d05c8516ec" xlink:to="loc_pcrx_EarningsPerShareBasicAndDilutedEPSAbstract_019cb481-9f12-7ab0-80e5-b3df11f79893" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareBasic_019cb481-9f12-71e8-8d10-ee088f7462e4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareBasic"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pcrx_EarningsPerShareBasicAndDilutedEPSAbstract_019cb481-9f12-7ab0-80e5-b3df11f79893" xlink:to="loc_us-gaap_EarningsPerShareBasic_019cb481-9f12-71e8-8d10-ee088f7462e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EarningsPerShareDiluted_019cb481-9f12-7cfe-ab00-ac1a8848a22b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EarningsPerShareDiluted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pcrx_EarningsPerShareBasicAndDilutedEPSAbstract_019cb481-9f12-7ab0-80e5-b3df11f79893" xlink:to="loc_us-gaap_EarningsPerShareDiluted_019cb481-9f12-7cfe-ab00-ac1a8848a22b" xlink:type="arc" order="2"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/NETINCOMEPERCOMMONSHAREScheduleofAntidilutiveSecuritiesDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#NETINCOMEPERCOMMONSHAREScheduleofAntidilutiveSecuritiesDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/NETINCOMEPERCOMMONSHAREScheduleofAntidilutiveSecuritiesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019cb481-9f12-7189-b8b8-4bb91b1c1a74" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019cb481-9f12-794a-91d0-70061bfc7b22" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019cb481-9f12-7189-b8b8-4bb91b1c1a74" xlink:to="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019cb481-9f12-794a-91d0-70061bfc7b22" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019cb481-9f12-797e-b221-d472b25a5bc9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfAntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareTable_019cb481-9f12-794a-91d0-70061bfc7b22" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019cb481-9f12-797e-b221-d472b25a5bc9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019cb481-9f12-797e-b221-d472b25a5bc9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019cb481-9f12-797e-b221-d472b25a5bc9" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019cb481-9f12-797e-b221-d472b25a5bc9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019cb481-9f12-7c91-ab76-f7b52641df99" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis_019cb481-9f12-797e-b221-d472b25a5bc9" xlink:to="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019cb481-9f12-7c91-ab76-f7b52641df99" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockOptionMember_019cb481-9f12-73ee-85de-9380516baa6c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockOptionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019cb481-9f12-7c91-ab76-f7b52641df99" xlink:to="loc_us-gaap_EmployeeStockOptionMember_019cb481-9f12-73ee-85de-9380516baa6c" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SeniorNotesMember_019cb481-9f12-789a-a39f-af0baaba83c4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SeniorNotesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019cb481-9f12-7c91-ab76-f7b52641df99" xlink:to="loc_us-gaap_SeniorNotesMember_019cb481-9f12-789a-a39f-af0baaba83c4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RestrictedStockUnitsRSUMember_019cb481-9f12-7b3d-a785-4049b5b92f22" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RestrictedStockUnitsRSUMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019cb481-9f12-7c91-ab76-f7b52641df99" xlink:to="loc_us-gaap_RestrictedStockUnitsRSUMember_019cb481-9f12-7b3d-a785-4049b5b92f22" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EmployeeStockMember_019cb481-9f12-7347-92ce-26f511ccbe70" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EmployeeStockMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesNameDomain_019cb481-9f12-7c91-ab76-f7b52641df99" xlink:to="loc_us-gaap_EmployeeStockMember_019cb481-9f12-7347-92ce-26f511ccbe70" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019cb481-9f12-709a-a38c-5d2f18a8b6a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareLineItems_019cb481-9f12-7189-b8b8-4bb91b1c1a74" xlink:to="loc_us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount_019cb481-9f12-709a-a38c-5d2f18a8b6a3" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/COMMITMENTSANDCONTINGENCIESDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#COMMITMENTSANDCONTINGENCIESDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/COMMITMENTSANDCONTINGENCIESDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingenciesTable_019cb481-9f12-706e-bca1-8f6b267134b0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingenciesTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_us-gaap_LossContingenciesTable_019cb481-9f12-706e-bca1-8f6b267134b0" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseAxis_019dae7e-9f2b-7ed4-9439-9256f767e1b9" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_LitigationCaseAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019cb481-9f12-706e-bca1-8f6b267134b0" xlink:to="loc_srt_LitigationCaseAxis_019dae7e-9f2b-7ed4-9439-9256f767e1b9" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_019dae7e-9f2b-7ed4-9439-9256f767e1b9_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_LitigationCaseAxis_019dae7e-9f2b-7ed4-9439-9256f767e1b9" xlink:to="loc_srt_LitigationCaseTypeDomain_019dae7e-9f2b-7ed4-9439-9256f767e1b9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_LitigationCaseTypeDomain_019dae7e-9f2b-7ba8-912f-67bcaf75821e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_LitigationCaseTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_LitigationCaseAxis_019dae7e-9f2b-7ed4-9439-9256f767e1b9" xlink:to="loc_srt_LitigationCaseTypeDomain_019dae7e-9f2b-7ba8-912f-67bcaf75821e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_MyoScienceMilestoneLitigationMember_019dae7e-9f2b-75f0-8a66-c70c9b945522" xlink:href="pcrx-20260331.xsd#pcrx_MyoScienceMilestoneLitigationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_LitigationCaseTypeDomain_019dae7e-9f2b-7ba8-912f-67bcaf75821e" xlink:to="loc_pcrx_MyoScienceMilestoneLitigationMember_019dae7e-9f2b-75f0-8a66-c70c9b945522" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ResearchDevelopmentFoundationMember_019dae7f-398a-7e91-81d4-cabc4455e803" xlink:href="pcrx-20260331.xsd#pcrx_ResearchDevelopmentFoundationMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_LitigationCaseTypeDomain_019dae7e-9f2b-7ba8-912f-67bcaf75821e" xlink:to="loc_pcrx_ResearchDevelopmentFoundationMember_019dae7f-398a-7e91-81d4-cabc4455e803" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_TypeOfArrangementAxis_019dae7f-398a-73e3-87b4-5a4a9759c87d" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_TypeOfArrangementAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019cb481-9f12-706e-bca1-8f6b267134b0" xlink:to="loc_us-gaap_TypeOfArrangementAxis_019dae7f-398a-73e3-87b4-5a4a9759c87d" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019dae7f-398a-73e3-87b4-5a4a9759c87d_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019dae7f-398a-73e3-87b4-5a4a9759c87d" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019dae7f-398a-73e3-87b4-5a4a9759c87d_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019dae7f-398a-74ed-bfe0-25d6310f61c0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ArrangementsAndNonarrangementTransactionsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_TypeOfArrangementAxis_019dae7f-398a-73e3-87b4-5a4a9759c87d" xlink:to="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019dae7f-398a-74ed-bfe0-25d6310f61c0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_LGChemPartnershipAgreementMember_019dae7f-398a-7cec-953c-b10d4d29592b" xlink:href="pcrx-20260331.xsd#pcrx_LGChemPartnershipAgreementMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ArrangementsAndNonarrangementTransactionsMember_019dae7f-398a-74ed-bfe0-25d6310f61c0" xlink:to="loc_pcrx_LGChemPartnershipAgreementMember_019dae7f-398a-7cec-953c-b10d4d29592b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_CounterpartyNameAxis_019dae7f-624f-7744-8965-0364b71277f6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_CounterpartyNameAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019cb481-9f12-706e-bca1-8f6b267134b0" xlink:to="loc_srt_CounterpartyNameAxis_019dae7f-624f-7744-8965-0364b71277f6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dae7f-624f-7744-8965-0364b71277f6_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_CounterpartyNameAxis_019dae7f-624f-7744-8965-0364b71277f6" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dae7f-624f-7744-8965-0364b71277f6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dae7f-624f-7d6f-aa0c-f0cb83fc96e4" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RepurchaseAgreementCounterpartyNameDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_CounterpartyNameAxis_019dae7f-624f-7744-8965-0364b71277f6" xlink:to="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dae7f-624f-7d6f-aa0c-f0cb83fc96e4" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_JohnsonJohnsonMedTechMember_019dae7f-624f-7e05-98ed-cbed9fae5903" xlink:href="pcrx-20260331.xsd#pcrx_JohnsonJohnsonMedTechMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dae7f-624f-7d6f-aa0c-f0cb83fc96e4" xlink:to="loc_pcrx_JohnsonJohnsonMedTechMember_019dae7f-624f-7e05-98ed-cbed9fae5903" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_GeneQuineMember_019dae7f-8c9a-7d8f-a593-24af2174f421" xlink:href="pcrx-20260331.xsd#pcrx_GeneQuineMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dae7f-624f-7d6f-aa0c-f0cb83fc96e4" xlink:to="loc_pcrx_GeneQuineMember_019dae7f-8c9a-7d8f-a593-24af2174f421" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_BaylorCollegeOfMedicineBaylorMember_019dae7f-8c9a-7abc-a117-fe03a1b1dd55" xlink:href="pcrx-20260331.xsd#pcrx_BaylorCollegeOfMedicineBaylorMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RepurchaseAgreementCounterpartyNameDomain_019dae7f-624f-7d6f-aa0c-f0cb83fc96e4" xlink:to="loc_pcrx_BaylorCollegeOfMedicineBaylorMember_019dae7f-8c9a-7abc-a117-fe03a1b1dd55" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductOrServiceAxis_019dae7f-624f-7114-aa4e-3aff281da5f5" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductOrServiceAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019cb481-9f12-706e-bca1-8f6b267134b0" xlink:to="loc_srt_ProductOrServiceAxis_019dae7f-624f-7114-aa4e-3aff281da5f5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019dae7f-624f-7114-aa4e-3aff281da5f5_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_ProductOrServiceAxis_019dae7f-624f-7114-aa4e-3aff281da5f5" xlink:to="loc_srt_ProductsAndServicesDomain_019dae7f-624f-7114-aa4e-3aff281da5f5_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_ProductsAndServicesDomain_019dae7f-624f-7a1a-863c-bbb9719229a6" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_ProductsAndServicesDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_ProductOrServiceAxis_019dae7f-624f-7114-aa4e-3aff281da5f5" xlink:to="loc_srt_ProductsAndServicesDomain_019dae7f-624f-7a1a-863c-bbb9719229a6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ZILRETTAMember_019dae7f-624f-7e06-a8d9-4afb6fb173c7" xlink:href="pcrx-20260331.xsd#pcrx_ZILRETTAMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_ProductsAndServicesDomain_019dae7f-624f-7a1a-863c-bbb9719229a6" xlink:to="loc_pcrx_ZILRETTAMember_019dae7f-624f-7e06-a8d9-4afb6fb173c7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_AchievementOfMilestoneAxis_019dae7f-8c9a-77ee-9212-5996fbfcc181" xlink:href="pcrx-20260331.xsd#pcrx_AchievementOfMilestoneAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019cb481-9f12-706e-bca1-8f6b267134b0" xlink:to="loc_pcrx_AchievementOfMilestoneAxis_019dae7f-8c9a-77ee-9212-5996fbfcc181" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_AchievementOfMilestoneDomain_019dae7f-8c9a-77ee-9212-5996fbfcc181_default" xlink:href="pcrx-20260331.xsd#pcrx_AchievementOfMilestoneDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_pcrx_AchievementOfMilestoneAxis_019dae7f-8c9a-77ee-9212-5996fbfcc181" xlink:to="loc_pcrx_AchievementOfMilestoneDomain_019dae7f-8c9a-77ee-9212-5996fbfcc181_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_AchievementOfMilestoneDomain_019dae7f-8c9a-779b-b709-eb5f9e497cb6" xlink:href="pcrx-20260331.xsd#pcrx_AchievementOfMilestoneDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_pcrx_AchievementOfMilestoneAxis_019dae7f-8c9a-77ee-9212-5996fbfcc181" xlink:to="loc_pcrx_AchievementOfMilestoneDomain_019dae7f-8c9a-779b-b709-eb5f9e497cb6" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_AchievementOfDevelopmentAndRegulatoryMilestonesMember_019dae7f-8c9a-7346-81b1-e2ad958c1875" xlink:href="pcrx-20260331.xsd#pcrx_AchievementOfDevelopmentAndRegulatoryMilestonesMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pcrx_AchievementOfMilestoneDomain_019dae7f-8c9a-779b-b709-eb5f9e497cb6" xlink:to="loc_pcrx_AchievementOfDevelopmentAndRegulatoryMilestonesMember_019dae7f-8c9a-7346-81b1-e2ad958c1875" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_InitiationOfAPhase2ClinicalTrialMember_019dae7f-8c9a-78f9-885d-1e97bbfcee80" xlink:href="pcrx-20260331.xsd#pcrx_InitiationOfAPhase2ClinicalTrialMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pcrx_AchievementOfMilestoneDomain_019dae7f-8c9a-779b-b709-eb5f9e497cb6" xlink:to="loc_pcrx_InitiationOfAPhase2ClinicalTrialMember_019dae7f-8c9a-78f9-885d-1e97bbfcee80" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_DevelopmentAndGlobalRegulatoryApprovalMilestonePaymentsMember_019dae7f-8c9a-7180-9fae-3fb864c11bcc" xlink:href="pcrx-20260331.xsd#pcrx_DevelopmentAndGlobalRegulatoryApprovalMilestonePaymentsMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_pcrx_AchievementOfMilestoneDomain_019dae7f-8c9a-779b-b709-eb5f9e497cb6" xlink:to="loc_pcrx_DevelopmentAndGlobalRegulatoryApprovalMilestonePaymentsMember_019dae7f-8c9a-7180-9fae-3fb864c11bcc" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_LegalEntityAxis_019dae7f-8c9a-7094-9938-dc5490f63b4b" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_LegalEntityAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019cb481-9f12-706e-bca1-8f6b267134b0" xlink:to="loc_dei_LegalEntityAxis_019dae7f-8c9a-7094-9938-dc5490f63b4b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dae7f-8c9a-7094-9938-dc5490f63b4b_default" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_dei_LegalEntityAxis_019dae7f-8c9a-7094-9938-dc5490f63b4b" xlink:to="loc_dei_EntityDomain_019dae7f-8c9a-7094-9938-dc5490f63b4b_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_dei_EntityDomain_019dae7f-8c9a-71fc-88f4-f591be393947" xlink:href="https://xbrl.sec.gov/dei/2025/dei-2025.xsd#dei_EntityDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_dei_LegalEntityAxis_019dae7f-8c9a-7094-9938-dc5490f63b4b" xlink:to="loc_dei_EntityDomain_019dae7f-8c9a-71fc-88f4-f591be393947" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_FlexionTherapeuticsIncMember_019dae7f-8c9a-7789-8442-2e50441cf3e7" xlink:href="pcrx-20260331.xsd#pcrx_FlexionTherapeuticsIncMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_dei_EntityDomain_019dae7f-8c9a-71fc-88f4-f591be393947" xlink:to="loc_pcrx_FlexionTherapeuticsIncMember_019dae7f-8c9a-7789-8442-2e50441cf3e7" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipAxis_019dae7f-8c9a-75c1-a87b-092dae35dab0" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019cb481-9f12-706e-bca1-8f6b267134b0" xlink:to="loc_srt_OwnershipAxis_019dae7f-8c9a-75c1-a87b-092dae35dab0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019dae7f-8c9a-75c1-a87b-092dae35dab0_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_OwnershipAxis_019dae7f-8c9a-75c1-a87b-092dae35dab0" xlink:to="loc_srt_OwnershipDomain_019dae7f-8c9a-75c1-a87b-092dae35dab0_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_OwnershipDomain_019dae7f-8c9a-7c90-9e64-028d74d0ac3b" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_OwnershipDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_OwnershipAxis_019dae7f-8c9a-75c1-a87b-092dae35dab0" xlink:to="loc_srt_OwnershipDomain_019dae7f-8c9a-7c90-9e64-028d74d0ac3b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_GQBioTherapeuticsGmbHMember_019dae7f-8c9a-78a8-976a-43b9843d3720" xlink:href="pcrx-20260331.xsd#pcrx_GQBioTherapeuticsGmbHMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_OwnershipDomain_019dae7f-8c9a-7c90-9e64-028d74d0ac3b" xlink:to="loc_pcrx_GQBioTherapeuticsGmbHMember_019dae7f-8c9a-78a8-976a-43b9843d3720" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019dae7f-8c9a-71c0-9e05-3714740d7574" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019cb481-9f12-706e-bca1-8f6b267134b0" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019dae7f-8c9a-71c0-9e05-3714740d7574" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dae7f-8c9a-71c0-9e05-3714740d7574_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019dae7f-8c9a-71c0-9e05-3714740d7574" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dae7f-8c9a-71c0-9e05-3714740d7574_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dae7f-8c9a-7f91-84cd-fba7138efc30" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019dae7f-8c9a-71c0-9e05-3714740d7574" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dae7f-8c9a-7f91-84cd-fba7138efc30" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_GQBioTherapeuticsGmbHMember_019dae7f-8c9a-7bf9-9e0a-5538301304b9" xlink:href="pcrx-20260331.xsd#pcrx_GQBioTherapeuticsGmbHMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dae7f-8c9a-7f91-84cd-fba7138efc30" xlink:to="loc_pcrx_GQBioTherapeuticsGmbHMember_019dae7f-8c9a-7bf9-9e0a-5538301304b9" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeAxis_019dae7f-8c9a-7276-9cd0-4b6e0ab08f4c" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_LossContingenciesTable_019cb481-9f12-706e-bca1-8f6b267134b0" xlink:to="loc_srt_RangeAxis_019dae7f-8c9a-7276-9cd0-4b6e0ab08f4c" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019dae7f-8c9a-7276-9cd0-4b6e0ab08f4c_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_RangeAxis_019dae7f-8c9a-7276-9cd0-4b6e0ab08f4c" xlink:to="loc_srt_RangeMember_019dae7f-8c9a-7276-9cd0-4b6e0ab08f4c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_RangeMember_019dae7f-8c9a-7646-9c81-aad17ba8939e" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_RangeMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_RangeAxis_019dae7f-8c9a-7276-9cd0-4b6e0ab08f4c" xlink:to="loc_srt_RangeMember_019dae7f-8c9a-7646-9c81-aad17ba8939e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MinimumMember_019dae7f-8c9a-7f38-ad86-f7c4f4b5035f" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MinimumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019dae7f-8c9a-7646-9c81-aad17ba8939e" xlink:to="loc_srt_MinimumMember_019dae7f-8c9a-7f38-ad86-f7c4f4b5035f" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_MaximumMember_019dae7f-8c9a-795c-aa2f-dabaf77ff971" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_MaximumMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_RangeMember_019dae7f-8c9a-7646-9c81-aad17ba8939e" xlink:to="loc_srt_MaximumMember_019dae7f-8c9a-795c-aa2f-dabaf77ff971" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementAmountAwardedFromOtherParty_019d205a-077a-75e5-a5f6-2b314b8fac74" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LitigationSettlementAmountAwardedFromOtherParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_us-gaap_LitigationSettlementAmountAwardedFromOtherParty_019d205a-077a-75e5-a5f6-2b314b8fac74" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_LitigationSettlementVolumeLimitedIncreasePeriod_019d205a-36a0-703e-bed9-c4b72b498e79" xlink:href="pcrx-20260331.xsd#pcrx_LitigationSettlementVolumeLimitedIncreasePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_pcrx_LitigationSettlementVolumeLimitedIncreasePeriod_019d205a-36a0-703e-bed9-c4b72b498e79" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_LitigationSettlementVolumeLimitedNumberOfModerateIncreasePeriods_019d205a-36a0-70ae-8667-f14265452c01" xlink:href="pcrx-20260331.xsd#pcrx_LitigationSettlementVolumeLimitedNumberOfModerateIncreasePeriods"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_pcrx_LitigationSettlementVolumeLimitedNumberOfModerateIncreasePeriods_019d205a-36a0-70ae-8667-f14265452c01" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_LitigationSettlementVolumeLimitedMaximumPercentagePeriod_019d205a-36a0-73dc-a8d7-9023aecb0848" xlink:href="pcrx-20260331.xsd#pcrx_LitigationSettlementVolumeLimitedMaximumPercentagePeriod"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_pcrx_LitigationSettlementVolumeLimitedMaximumPercentagePeriod_019d205a-36a0-73dc-a8d7-9023aecb0848" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementLoss_019d205a-36a0-7c85-8744-c41e8bcb89b5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LitigationSettlementLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_us-gaap_LitigationSettlementLoss_019d205a-36a0-7c85-8744-c41e8bcb89b5" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_NumberOfParagraphIVCertifications_019d205a-36a0-76c6-a063-713918fb4528" xlink:href="pcrx-20260331.xsd#pcrx_NumberOfParagraphIVCertifications"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_pcrx_NumberOfParagraphIVCertifications_019d205a-36a0-76c6-a063-713918fb4528" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_NumberOfGenericDrugManufacturers_019d205a-36a0-7ded-b7b1-f3eb54afd40b" xlink:href="pcrx-20260331.xsd#pcrx_NumberOfGenericDrugManufacturers"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_pcrx_NumberOfGenericDrugManufacturers_019d205a-36a0-7ded-b7b1-f3eb54afd40b" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_LitigationSettlementAmountExpectedToBeAwardedFromOtherParty_019d205a-6d57-7b05-bfe3-2828adad1364" xlink:href="pcrx-20260331.xsd#pcrx_LitigationSettlementAmountExpectedToBeAwardedFromOtherParty"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_pcrx_LitigationSettlementAmountExpectedToBeAwardedFromOtherParty_019d205a-6d57-7b05-bfe3-2828adad1364" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementInterest_019d205a-6d57-7a3f-ba98-10b858a3498b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LitigationSettlementInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_us-gaap_LitigationSettlementInterest_019d205a-6d57-7a3f-ba98-10b858a3498b" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ProceedsFromLegalSettlements_019d205a-6d57-7fe2-9b04-ad139b04e976" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ProceedsFromLegalSettlements"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_us-gaap_ProceedsFromLegalSettlements_019d205a-6d57-7fe2-9b04-ad139b04e976" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LossContingencyPendingClaimsNumber_019d205a-6d57-78c5-8b50-338d96a653d5" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LossContingencyPendingClaimsNumber"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_us-gaap_LossContingencyPendingClaimsNumber_019d205a-6d57-78c5-8b50-338d96a653d5" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ContractWithCustomerLiability_019dae5d-6be1-7368-8e66-c69cdbcb9414" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ContractWithCustomerLiability"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_us-gaap_ContractWithCustomerLiability_019dae5d-6be1-7368-8e66-c69cdbcb9414" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ContractualObligationMinimumMonthlyCommissionDuration_019d205a-8c40-726e-a714-56fd3ea0b9db" xlink:href="pcrx-20260331.xsd#pcrx_ContractualObligationMinimumMonthlyCommissionDuration"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_pcrx_ContractualObligationMinimumMonthlyCommissionDuration_019d205a-8c40-726e-a714-56fd3ea0b9db" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ContractualObligationMutualTerminationRightsTerm_019d205a-8c40-7753-9c89-a0e23f621173" xlink:href="pcrx-20260331.xsd#pcrx_ContractualObligationMutualTerminationRightsTerm"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_pcrx_ContractualObligationMutualTerminationRightsTerm_019d205a-8c40-7753-9c89-a0e23f621173" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_CollaborativeArrangementMilestonePaymentsToBeReceivedMaximum_019d205a-b559-757e-9817-0c7bf93d03fd" xlink:href="pcrx-20260331.xsd#pcrx_CollaborativeArrangementMilestonePaymentsToBeReceivedMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_pcrx_CollaborativeArrangementMilestonePaymentsToBeReceivedMaximum_019d205a-b559-757e-9817-0c7bf93d03fd" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019d205a-b559-7754-a9c7-99c1e69ca3e3" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_us-gaap_BusinessAcquisitionPercentageOfVotingInterestsAcquired_019d205a-b559-7754-a9c7-99c1e69ca3e3" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_RevenueFromContractWithCustomerMilestonePaymentsMaximum_019d205a-b559-73ce-8b25-158a7020b3ed" xlink:href="pcrx-20260331.xsd#pcrx_RevenueFromContractWithCustomerMilestonePaymentsMaximum"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_LossContingenciesLineItems_019cb481-9f12-7fde-93f1-833cb09ad5a3" xlink:to="loc_pcrx_RevenueFromContractWithCustomerMilestonePaymentsMaximum_019d205a-b559-73ce-8b25-158a7020b3ed" xlink:type="arc" order="16"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/SEGMENTINFORMATIONNarrativeDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#SEGMENTINFORMATIONNarrativeDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/SEGMENTINFORMATIONNarrativeDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_019dae77-9fde-7bb1-a294-660d1fdf2b87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_EntityWideRevenueMajorCustomerLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_019dae77-446d-70d7-ba83-8b074f5a400f" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_019dae77-9fde-7bb1-a294-660d1fdf2b87" xlink:to="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_019dae77-446d-70d7-ba83-8b074f5a400f" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_StatementGeographicalAxis_019dae77-cf14-7941-8004-e969a2716234" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_StatementGeographicalAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_019dae77-446d-70d7-ba83-8b074f5a400f" xlink:to="loc_srt_StatementGeographicalAxis_019dae77-cf14-7941-8004-e969a2716234" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019dae77-cf14-7941-8004-e969a2716234_default" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_srt_StatementGeographicalAxis_019dae77-cf14-7941-8004-e969a2716234" xlink:to="loc_srt_SegmentGeographicalDomain_019dae77-cf14-7941-8004-e969a2716234_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_srt_SegmentGeographicalDomain_019dae77-cf14-7ace-8ce6-2b8dfd95fbf8" xlink:href="https://xbrl.fasb.org/srt/2025/elts/srt-2025.xsd#srt_SegmentGeographicalDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_srt_StatementGeographicalAxis_019dae77-cf14-7941-8004-e969a2716234" xlink:to="loc_srt_SegmentGeographicalDomain_019dae77-cf14-7ace-8ce6-2b8dfd95fbf8" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_US_019dae77-cf14-796e-a5a7-0adc6446bbfd" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_US"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019dae77-cf14-7ace-8ce6-2b8dfd95fbf8" xlink:to="loc_country_US_019dae77-cf14-796e-a5a7-0adc6446bbfd" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_DE_019dae77-cf14-77ed-a371-efa7e11aaad0" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_DE"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019dae77-cf14-7ace-8ce6-2b8dfd95fbf8" xlink:to="loc_country_DE_019dae77-cf14-77ed-a371-efa7e11aaad0" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_country_GB_019dae77-cf14-7932-8aae-ffddc9cbe4b8" xlink:href="https://xbrl.sec.gov/country/2025/country-2025.xsd#country_GB"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_srt_SegmentGeographicalDomain_019dae77-cf14-7ace-8ce6-2b8dfd95fbf8" xlink:to="loc_country_GB_019dae77-cf14-7932-8aae-ffddc9cbe4b8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019dae77-cf14-7453-bea9-501339d688d4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByBenchmarkAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_019dae77-446d-70d7-ba83-8b074f5a400f" xlink:to="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019dae77-cf14-7453-bea9-501339d688d4" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019dae77-cf14-7453-bea9-501339d688d4_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019dae77-cf14-7453-bea9-501339d688d4" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019dae77-cf14-7453-bea9-501339d688d4_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019dae77-cf14-7eec-aef0-683cd7e5df6e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskBenchmarkDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByBenchmarkAxis_019dae77-cf14-7453-bea9-501339d688d4" xlink:to="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019dae77-cf14-7eec-aef0-683cd7e5df6e" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_PropertyPlantAndEquipmentMember_019dae77-cf14-7f1e-8bfb-87b10814a5ab" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_PropertyPlantAndEquipmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskBenchmarkDomain_019dae77-cf14-7eec-aef0-683cd7e5df6e" xlink:to="loc_us-gaap_PropertyPlantAndEquipmentMember_019dae77-cf14-7f1e-8bfb-87b10814a5ab" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskByTypeAxis_019dae77-cf14-70a8-89d7-d332e36011d6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskByTypeAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ScheduleOfEntityWideRevenueByMajorCustomersByReportingSegmentsTable_019dae77-446d-70d7-ba83-8b074f5a400f" xlink:to="loc_us-gaap_ConcentrationRiskByTypeAxis_019dae77-cf14-70a8-89d7-d332e36011d6" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019dae77-cf14-70a8-89d7-d332e36011d6_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019dae77-cf14-70a8-89d7-d332e36011d6" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019dae77-cf14-70a8-89d7-d332e36011d6_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskTypeDomain_019dae77-cf14-788c-bcb7-951b1c505975" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskTypeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_ConcentrationRiskByTypeAxis_019dae77-cf14-70a8-89d7-d332e36011d6" xlink:to="loc_us-gaap_ConcentrationRiskTypeDomain_019dae77-cf14-788c-bcb7-951b1c505975" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_GeographicConcentrationRiskMember_019dae77-cf14-7645-b4d3-54ef72600149" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_GeographicConcentrationRiskMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_ConcentrationRiskTypeDomain_019dae77-cf14-788c-bcb7-951b1c505975" xlink:to="loc_us-gaap_GeographicConcentrationRiskMember_019dae77-cf14-7645-b4d3-54ef72600149" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ConcentrationRiskPercentage1_019dae77-cf14-7801-afb6-a9aad218b3fa" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ConcentrationRiskPercentage1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_EntityWideRevenueMajorCustomerLineItems_019dae77-9fde-7bb1-a294-660d1fdf2b87" xlink:to="loc_us-gaap_ConcentrationRiskPercentage1_019dae77-cf14-7801-afb6-a9aad218b3fa" xlink:type="arc" order="0"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://www.pacira.com/role/SEGMENTINFORMATIONScheduleofReconciliationofSignificantExpenseCategoriesDetails" xlink:type="simple" xlink:href="pcrx-20260331.xsd#SEGMENTINFORMATIONScheduleofReconciliationofSignificantExpenseCategoriesDetails"/>
  <link:definitionLink xlink:role="http://www.pacira.com/role/SEGMENTINFORMATIONScheduleofReconciliationofSignificantExpenseCategoriesDetails" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentReportingAssetReconcilingItemLineItems"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable_019cb481-9f12-7c22-b848-12f27b959d87" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/all" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable_019cb481-9f12-7c22-b848-12f27b959d87" xlink:type="arc" order="1" xbrldt:closed="true" xbrldt:contextElement="segment"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_StatementBusinessSegmentsAxis_019cb481-9f12-7942-b61b-e9e35750927c" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_StatementBusinessSegmentsAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable_019cb481-9f12-7c22-b848-12f27b959d87" xlink:to="loc_us-gaap_StatementBusinessSegmentsAxis_019cb481-9f12-7942-b61b-e9e35750927c" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019cb481-9f12-7942-b61b-e9e35750927c_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019cb481-9f12-7942-b61b-e9e35750927c" xlink:to="loc_us-gaap_SegmentDomain_019cb481-9f12-7942-b61b-e9e35750927c_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_SegmentDomain_019cb481-9f12-7f9f-a1db-69f73f8907dc" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_SegmentDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_StatementBusinessSegmentsAxis_019cb481-9f12-7942-b61b-e9e35750927c" xlink:to="loc_us-gaap_SegmentDomain_019cb481-9f12-7f9f-a1db-69f73f8907dc" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ReportableSegmentMember_019cb481-9f12-7c99-88da-8fda1f0423e6" xlink:href="pcrx-20260331.xsd#pcrx_ReportableSegmentMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentDomain_019cb481-9f12-7f9f-a1db-69f73f8907dc" xlink:to="loc_pcrx_ReportableSegmentMember_019cb481-9f12-7c99-88da-8fda1f0423e6" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAxis_019dae6f-2f96-75e9-bdee-379472baf3e9" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAxis"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/hypercube-dimension" xlink:from="loc_us-gaap_ReconciliationOfAssetsFromSegmentToConsolidatedTable_019cb481-9f12-7c22-b848-12f27b959d87" xlink:to="loc_us-gaap_BusinessAcquisitionAxis_019dae6f-2f96-75e9-bdee-379472baf3e9" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dae6f-2f96-75e9-bdee-379472baf3e9_default" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-default" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019dae6f-2f96-75e9-bdee-379472baf3e9" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dae6f-2f96-75e9-bdee-379472baf3e9_default" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dae6f-2f96-77ca-95ff-71ad6656800b" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessAcquisitionAcquireeDomain"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/dimension-domain" xlink:from="loc_us-gaap_BusinessAcquisitionAxis_019dae6f-2f96-75e9-bdee-379472baf3e9" xlink:to="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dae6f-2f96-77ca-95ff-71ad6656800b" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_GQBioAcquisitionMember_019dae6f-2f96-7d9c-a728-5a1c0d1ac57b" xlink:href="pcrx-20260331.xsd#pcrx_GQBioAcquisitionMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_BusinessAcquisitionAcquireeDomain_019dae6f-2f96-77ca-95ff-71ad6656800b" xlink:to="loc_pcrx_GQBioAcquisitionMember_019dae6f-2f96-7d9c-a728-5a1c0d1ac57b" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019cb481-9f12-71dd-ae8f-e98507b3aaa4" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax_019cb481-9f12-71dd-ae8f-e98507b3aaa4" xlink:type="arc" order="0"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_CostOfGoodsSoldAdjusted_019cb481-9f12-7e85-ac69-4e57b5e328c5" xlink:href="pcrx-20260331.xsd#pcrx_CostOfGoodsSoldAdjusted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_pcrx_CostOfGoodsSoldAdjusted_019cb481-9f12-7e85-ac69-4e57b5e328c5" xlink:type="arc" order="1"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_ResearchAndDevelopmentAdjusted_019cb481-9f12-7fae-b05e-f28c9d6cf0c8" xlink:href="pcrx-20260331.xsd#pcrx_ResearchAndDevelopmentAdjusted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_pcrx_ResearchAndDevelopmentAdjusted_019cb481-9f12-7fae-b05e-f28c9d6cf0c8" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_SellingAndMarketingAdjusted_019cb481-9f12-7c49-b550-0e2fd5fe5f1d" xlink:href="pcrx-20260331.xsd#pcrx_SellingAndMarketingAdjusted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_pcrx_SellingAndMarketingAdjusted_019cb481-9f12-7c49-b550-0e2fd5fe5f1d" xlink:type="arc" order="3"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_SellingGeneralAndAdministrativeAdjusted_019cb481-9f12-750d-9245-45e78d4f41b3" xlink:href="pcrx-20260331.xsd#pcrx_SellingGeneralAndAdministrativeAdjusted"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_pcrx_SellingGeneralAndAdministrativeAdjusted_019cb481-9f12-750d-9245-45e78d4f41b3" xlink:type="arc" order="4"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_ShareBasedCompensation_019cb481-9f12-75e0-94cd-9a86bab068b6" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ShareBasedCompensation"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_us-gaap_ShareBasedCompensation_019cb481-9f12-75e0-94cd-9a86bab068b6" xlink:type="arc" order="5"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_AmortizationOfIntangibleAssets_019cb481-9f12-76d5-be00-9955d0e48421" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_AmortizationOfIntangibleAssets"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_us-gaap_AmortizationOfIntangibleAssets_019cb481-9f12-76d5-be00-9955d0e48421" xlink:type="arc" order="6"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_019cb481-9f12-7c17-9bbd-b8a55573f5d0" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_us-gaap_BusinessCombinationContingentConsiderationArrangementsChangeInAmountOfContingentConsiderationLiability1_019cb481-9f12-7c17-9bbd-b8a55573f5d0" xlink:type="arc" order="7"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_LitigationSettlementLoss_019cb481-9f12-77f2-9221-a15cda703b6e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_LitigationSettlementLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_us-gaap_LitigationSettlementLoss_019cb481-9f12-77f2-9221-a15cda703b6e" xlink:type="arc" order="8"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_OtherCostOfOperatingRevenue_019cb481-9f12-7120-9a57-941e47960aeb" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_OtherCostOfOperatingRevenue"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_us-gaap_OtherCostOfOperatingRevenue_019cb481-9f12-7120-9a57-941e47960aeb" xlink:type="arc" order="9"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_CostsAndExpenses_019cb481-9f12-70cc-8f6b-e43fa477842e" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_CostsAndExpenses"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_us-gaap_CostsAndExpenses_019cb481-9f12-70cc-8f6b-e43fa477842e" xlink:type="arc" order="10"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NonoperatingIncomeExpense_019cb481-9f12-73cf-93d4-671b5517be32" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NonoperatingIncomeExpense"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_us-gaap_NonoperatingIncomeExpense_019cb481-9f12-73cf-93d4-671b5517be32" xlink:type="arc" order="11"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019cb481-9f12-7954-b075-5cf4e7da4ebd" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_us-gaap_IncomeLossFromContinuingOperationsBeforeIncomeTaxesExtraordinaryItemsNoncontrollingInterest_019cb481-9f12-7954-b075-5cf4e7da4ebd" xlink:type="arc" order="12"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_IncomeTaxExpenseBenefit_019cb481-9f12-7f9c-bffd-8ab0aa9aebb2" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_IncomeTaxExpenseBenefit"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_us-gaap_IncomeTaxExpenseBenefit_019cb481-9f12-7f9c-bffd-8ab0aa9aebb2" xlink:type="arc" order="13"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_NetIncomeLoss_019cb481-9f12-7bb9-873d-84adac555384" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_NetIncomeLoss"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_us-gaap_NetIncomeLoss_019cb481-9f12-7bb9-873d-84adac555384" xlink:type="arc" order="14"/>
    <link:loc xlink:type="locator" xlink:label="loc_us-gaap_BusinessCombinationLiabilitiesArisingFromContingenciesAmountRecognized_019dae6f-2f96-7739-b848-8cd84f96e287" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_BusinessCombinationLiabilitiesArisingFromContingenciesAmountRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_us-gaap_BusinessCombinationLiabilitiesArisingFromContingenciesAmountRecognized_019dae6f-2f96-7739-b848-8cd84f96e287" xlink:type="arc" order="15"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_BusinessCombinationContingencyRecognizedAtAcquisitionDateEmployeeCompensationLiabilityAssumedNumberOfEmployees_019dae6f-2f96-74d0-b0c5-5b1fc55113f3" xlink:href="pcrx-20260331.xsd#pcrx_BusinessCombinationContingencyRecognizedAtAcquisitionDateEmployeeCompensationLiabilityAssumedNumberOfEmployees"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_pcrx_BusinessCombinationContingencyRecognizedAtAcquisitionDateEmployeeCompensationLiabilityAssumedNumberOfEmployees_019dae6f-2f96-74d0-b0c5-5b1fc55113f3" xlink:type="arc" order="16"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_BusinessCombinationLiabilitiesArisingFromContingenciesPeriodOfRecognized_019dae6f-2f96-7785-8f1e-5fc2bf007307" xlink:href="pcrx-20260331.xsd#pcrx_BusinessCombinationLiabilitiesArisingFromContingenciesPeriodOfRecognized"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_pcrx_BusinessCombinationLiabilitiesArisingFromContingenciesPeriodOfRecognized_019dae6f-2f96-7785-8f1e-5fc2bf007307" xlink:type="arc" order="17"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_BusinessCombinationLiabilitiesArisingFromContingenciesPercentYearOne_019dae6f-2f96-73d3-82de-e05b4b2fa1dd" xlink:href="pcrx-20260331.xsd#pcrx_BusinessCombinationLiabilitiesArisingFromContingenciesPercentYearOne"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_pcrx_BusinessCombinationLiabilitiesArisingFromContingenciesPercentYearOne_019dae6f-2f96-73d3-82de-e05b4b2fa1dd" xlink:type="arc" order="18"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_BusinessCombinationLiabilitiesArisingFromContingenciesPercentYearTwo_019dae6f-2f96-7724-9e1e-160a076e8e5a" xlink:href="pcrx-20260331.xsd#pcrx_BusinessCombinationLiabilitiesArisingFromContingenciesPercentYearTwo"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_pcrx_BusinessCombinationLiabilitiesArisingFromContingenciesPercentYearTwo_019dae6f-2f96-7724-9e1e-160a076e8e5a" xlink:type="arc" order="19"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_BusinessCombinationLiabilitiesArisingFromContingenciesPercentYearThree_019dae6f-2f96-73aa-bc61-ef64f235df20" xlink:href="pcrx-20260331.xsd#pcrx_BusinessCombinationLiabilitiesArisingFromContingenciesPercentYearThree"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_us-gaap_SegmentReportingAssetReconcilingItemLineItems_019cb481-9f12-7b24-837c-e6f8e906e83e" xlink:to="loc_pcrx_BusinessCombinationLiabilitiesArisingFromContingenciesPercentYearThree_019dae6f-2f96-73aa-bc61-ef64f235df20" xlink:type="arc" order="20"/>
  </link:definitionLink>
  <link:roleRef roleURI="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#IndividualsOnly"/>
  <link:definitionLink xlink:role="http://xbrl.sec.gov/ecd/role/IndividualsOnly" xlink:type="extended">
    <link:loc xlink:type="locator" xlink:label="loc_ecd_AllIndividualsMember" xlink:href="https://xbrl.sec.gov/ecd/2025/ecd-2025.xsd#ecd_AllIndividualsMember"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_BrendanTeehanMember_019cb481-9d3e-7f2c-947a-8d8f75d4f214" xlink:href="pcrx-20260331.xsd#pcrx_BrendanTeehanMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_pcrx_BrendanTeehanMember_019cb481-9d3e-7f2c-947a-8d8f75d4f214" xlink:type="arc" order="2"/>
    <link:loc xlink:type="locator" xlink:label="loc_pcrx_LaurenRikerMember_019cb481-9d3e-71b9-9078-f58c2e268250" xlink:href="pcrx-20260331.xsd#pcrx_LaurenRikerMember"/>
    <link:definitionArc xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="loc_ecd_AllIndividualsMember" xlink:to="loc_pcrx_LaurenRikerMember_019cb481-9d3e-71b9-9078-f58c2e268250" xlink:type="arc" order="3"/>
  </link:definitionLink>
</link:linkbase>
