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  <xs:element id="ardx_ContractWithCustomerGrossToNetSalesAccrualRollForward" abstract="true" name="ContractWithCustomerGrossToNetSalesAccrualRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_ExitFee2022Member" abstract="true" name="ExitFee2022Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_CostOfRevenueAggregateAmountRecognized" abstract="false" name="CostOfRevenueAggregateAmountRecognized" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LoanAgreementExitFeeNetProductRevenueThresholdMetricTrailingSixMonthBasisMinimum" abstract="false" name="LoanAgreementExitFeeNetProductRevenueThresholdMetricTrailingSixMonthBasisMinimum" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_SaleOfStockWeightedAveragePricePerShare" abstract="false" name="SaleOfStockWeightedAveragePricePerShare" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:perShareItemType"/>
  <xs:element id="ardx_CollaborativeArrangementPotentialDevelopmentAndCommercializationMilestones" abstract="false" name="CollaborativeArrangementPotentialDevelopmentAndCommercializationMilestones" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_CollaborativeArrangementFeeReceivableForReductionInRoyaltyRate" abstract="false" name="CollaborativeArrangementFeeReceivableForReductionInRoyaltyRate" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_CashCashEquivalentsAndInvestmentsGrossUnrealizedGains" abstract="false" name="CashCashEquivalentsAndInvestmentsGrossUnrealizedGains" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_DebtInstrumentFeeDueUponMaturityAccelerationPrepaymentTerminationPercentage" abstract="false" name="DebtInstrumentFeeDueUponMaturityAccelerationPrepaymentTerminationPercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_DebtInstrumentPrepaymentFeePercentage" abstract="false" name="DebtInstrumentPrepaymentFeePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_LoanAgreementFutureObligationUponFundingOrOtherEvents" abstract="false" name="LoanAgreementFutureObligationUponFundingOrOtherEvents" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ContractWithCustomerGrossToNetSalesProvisions" abstract="false" name="ContractWithCustomerGrossToNetSalesProvisions" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_FairValueSensitivityAnalysisChangeInProbabilityOfOccurrencePercentage" abstract="false" name="FairValueSensitivityAnalysisChangeInProbabilityOfOccurrencePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_SecuredOvernightFinancingRateSOFRFloorRateMember" abstract="true" name="SecuredOvernightFinancingRateSOFRFloorRateMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_HealthCareRoyaltyPartnersIVLPMember" abstract="true" name="HealthCareRoyaltyPartnersIVLPMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasedPriceOfShare" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasedPriceOfShare" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:perShareItemType"/>
  <xs:element id="ardx_CollaborativeArrangementPotentialDevelopmentMilestones" abstract="false" name="CollaborativeArrangementPotentialDevelopmentMilestones" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_PercentageOfRoyaltyRevenue" abstract="false" name="PercentageOfRoyaltyRevenue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_IncreaseDecreaseInPrepaidCommercialManufacturingExpense" abstract="false" name="IncreaseDecreaseInPrepaidCommercialManufacturingExpense" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ExitFeePercentage" abstract="false" name="ExitFeePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityTransactionCosts" abstract="false" name="ContractWithCustomerLiabilityTransactionCosts" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_PercentageOfNonRoyaltyRevenue" abstract="false" name="PercentageOfNonRoyaltyRevenue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityRevenueInvoicedAsPrepaymentsForProductSupplyCurrent" abstract="false" name="ContractWithCustomerLiabilityRevenueInvoicedAsPrepaymentsForProductSupplyCurrent" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LoanAgreementCovenantNetProductRevenueAsPercentageOfOutstandingLoanBalanceMinimum" abstract="false" name="LoanAgreementCovenantNetProductRevenueAsPercentageOfOutstandingLoanBalanceMinimum" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types1:percentItemType"/>
  <xs:element id="ardx_TermLoan2018Member" abstract="true" name="TermLoan2018Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_BioRidgePharmaLLCMember" abstract="true" name="BioRidgePharmaLLCMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_AmerisourceBergenDrugCorporationMember" abstract="true" name="AmerisourceBergenDrugCorporationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
  <xs:element id="ardx_ProductSupplyRevenueMember" abstract="true" name="ProductSupplyRevenueMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types1:domainItemType"/>
</xs:schema>
