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  <xs:element id="ardx_PercentageOfRoyaltyRevenue" abstract="false" name="PercentageOfRoyaltyRevenue" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_FairValueSensitivityAnalysisChangeInProbabilityOfOccurrencePercentage" abstract="false" name="FairValueSensitivityAnalysisChangeInProbabilityOfOccurrencePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_TwoThousandFourteenEquityIncentiveAwardPlanMember" abstract="true" name="TwoThousandFourteenEquityIncentiveAwardPlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_CollaborationAndLicensingAgreementsUpfrontLicenseFees" abstract="false" name="CollaborationAndLicensingAgreementsUpfrontLicenseFees" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ExitFee2018Member" abstract="true" name="ExitFee2018Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_SharesAvailableForGrantRollForward" abstract="true" name="SharesAvailableForGrantRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_CollaborativeArrangementPotentialCommercializationMilestones" abstract="false" name="CollaborativeArrangementPotentialCommercializationMilestones" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_PrepaidCommercialManufacturingCurrent" abstract="false" name="PrepaidCommercialManufacturingCurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ChangeInContractWithCustomerLiabilityCurrentRollforwardRollForward" abstract="true" name="ChangeInContractWithCustomerLiabilityCurrentRollforwardRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_CollaborativeArrangementFeeReceivableForReductionInRoyaltyRateNumberOfPaymentTranches" abstract="false" name="CollaborativeArrangementFeeReceivableForReductionInRoyaltyRateNumberOfPaymentTranches" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="ardx_GoVersusRaabMember" abstract="true" name="GoVersusRaabMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_LesseeOperatingLeaseLiabilityToBePaidAfterYearFour" abstract="false" name="LesseeOperatingLeaseLiabilityToBePaidAfterYearFour" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <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_LoanAgreementCovenantNetProductRevenueAsPercentageOfOutstandingLoanBalanceMinimum" abstract="false" name="LoanAgreementCovenantNetProductRevenueAsPercentageOfOutstandingLoanBalanceMinimum" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_ContractWithCustomerDiscountsAndChargebacksMember" abstract="true" name="ContractWithCustomerDiscountsAndChargebacksMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_AccruedGrossToNetRevenueLiabilities" abstract="false" name="AccruedGrossToNetRevenueLiabilities" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_IncomeTaxDisclosureLineItems" abstract="true" name="IncomeTaxDisclosureLineItems" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_ContractWithCustomerGrossToNetSalesAccrualActivityDuringCurrentPeriod" abstract="false" name="ContractWithCustomerGrossToNetSalesAccrualActivityDuringCurrentPeriod" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_NumberOfSeparateCollaborativeAgreements" abstract="false" name="NumberOfSeparateCollaborativeAgreements" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="ardx_OperatingLossCarryforwardsWithoutExpiration" abstract="false" name="OperatingLossCarryforwardsWithoutExpiration" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDueToAuthorizedInPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDueToAuthorizedInPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_PotentialCommonSharesAntiDilutiveEffectOnSecurities" abstract="false" name="PotentialCommonSharesAntiDilutiveEffectOnSecurities" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_AccruedNonClinicalResearchAndDevelopmentExpenses" abstract="false" name="AccruedNonClinicalResearchAndDevelopmentExpenses" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_DebtInstrumentInterestPaymentExtensionTerm" abstract="false" name="DebtInstrumentInterestPaymentExtensionTerm" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="ardx_TwoThousandSixteenEmploymentCommencementIncentivePlanMember" abstract="true" name="TwoThousandSixteenEmploymentCommencementIncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasedPriceOfShare" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardPurchasedPriceOfShare" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="ardx_ChangeInContractWithCustomerLiabilityNoncurrentRollforwardRollForward" abstract="true" name="ChangeInContractWithCustomerLiabilityNoncurrentRollforwardRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_EmployeeStockPurchasePlanSharesAvailableRollForward" abstract="true" name="EmployeeStockPurchasePlanSharesAvailableRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantOptionsPurchases" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantOptionsPurchases" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_AuditInformationAbstract" abstract="true" name="AuditInformationAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_CollaborationAndLicensingAgreementsUpfrontLicenseFeesSecondInstallment" abstract="false" name="CollaborationAndLicensingAgreementsUpfrontLicenseFeesSecondInstallment" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LoanAgreementCovenantCashAndCashEquivalentsAsPercentageOfOutstandingLoanBalanceCalculationPeriod" abstract="false" name="LoanAgreementCovenantCashAndCashEquivalentsAsPercentageOfOutstandingLoanBalanceCalculationPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:durationItemType"/>
  <xs:element id="ardx_StockOptionsWeightedAverageRemainingContractualTermAbstract" abstract="true" name="StockOptionsWeightedAverageRemainingContractualTermAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_EmployeeStockPurchasePlanMember" abstract="true" name="EmployeeStockPurchasePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_MinimumTaxCreditCarryforwardMember" abstract="true" name="MinimumTaxCreditCarryforwardMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_LicenseAgreementDevelopmentCommercializationDistributionInCanadaMember" abstract="true" name="LicenseAgreementDevelopmentCommercializationDistributionInCanadaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_DebtInstrumentVariableRateBaseOption" abstract="false" name="DebtInstrumentVariableRateBaseOption" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_ShanghaiFosunPharmaceuticalIndustrialDevelopmentMember" abstract="true" name="ShanghaiFosunPharmaceuticalIndustrialDevelopmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <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_TaxAuthorityStatesOtherThanCaliforniaMember" abstract="true" name="TaxAuthorityStatesOtherThanCaliforniaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ScheduleOfGrossToNetSalesAccrualsTableTextBlock" abstract="false" name="ScheduleOfGrossToNetSalesAccrualsTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="ardx_DebtInstrumentVariableRatePlusOption" abstract="false" name="DebtInstrumentVariableRatePlusOption" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_DeferredRoyaltyObligationNoncurrent" abstract="false" name="DeferredRoyaltyObligationNoncurrent" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_IncreaseInSharesReservedForIssuanceMaximumSharesToBeIssuedUponInclusionOfForfeitedOrUnexercisedOptions" abstract="false" name="IncreaseInSharesReservedForIssuanceMaximumSharesToBeIssuedUponInclusionOfForfeitedOrUnexercisedOptions" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_ContractWithCustomerCopayAndReturnsMember" abstract="true" name="ContractWithCustomerCopayAndReturnsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_DeferredTaxAssetsAmortizationAndDepreciation" abstract="false" name="DeferredTaxAssetsAmortizationAndDepreciation" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_FacilityFremontCaliforniaMember" abstract="true" name="FacilityFremontCaliforniaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_AstraZenecaTerminationAgreementMember" abstract="true" name="AstraZenecaTerminationAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_StockIssuanceCostCommissionPercent" abstract="false" name="StockIssuanceCostCommissionPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_FairValueSensitivityAnalysisTenPercentChangeInProbabilityOfOccurrenceEffectOnValuation" abstract="false" name="FairValueSensitivityAnalysisTenPercentChangeInProbabilityOfOccurrenceEffectOnValuation" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_InvestmentsAndCashAmortizedCost" abstract="false" name="InvestmentsAndCashAmortizedCost" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ProceedsFromSaleOfFutureRoyaltiesNetOfIssuanceCosts" abstract="false" name="ProceedsFromSaleOfFutureRoyaltiesNetOfIssuanceCosts" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityRevenueRecognizedCashReceived" abstract="false" name="ContractWithCustomerLiabilityRevenueRecognizedCashReceived" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_DerivativeLiabilityForExitFees" abstract="false" name="DerivativeLiabilityForExitFees" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_AccruedResearchAndDevelopmentExpensesPolicyPolicyTextBlock" abstract="false" name="AccruedResearchAndDevelopmentExpensesPolicyPolicyTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="ardx_GrossToNetSalesAccrualAndReserveClassificationDomain" abstract="true" name="GrossToNetSalesAccrualAndReserveClassificationDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_DebtInstrumentInterestRateOnDefaultPercentage" abstract="false" name="DebtInstrumentInterestRateOnDefaultPercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_FacilityMilwaukeeWisconsinMember" abstract="true" name="FacilityMilwaukeeWisconsinMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantDecreaseDueToGrantedInPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantDecreaseDueToGrantedInPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_KnightTherapeuticsIncMember" abstract="true" name="KnightTherapeuticsIncMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_TermLoan2022AMember" abstract="true" name="TermLoan2022AMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_OfficeEquipmentAndFurnitureMember" abstract="true" name="OfficeEquipmentAndFurnitureMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_OpenMarketSalesAgreement2020AtTheMarketOfferingMember" abstract="true" name="OpenMarketSalesAgreement2020AtTheMarketOfferingMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_RemainingFundingBasedOnConditionalMilestoneAchievement" abstract="false" name="RemainingFundingBasedOnConditionalMilestoneAchievement" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_IncreaseInSharesReservedForIssuanceMaximumSharesToBeIssuedUponExerciseOfStockOptions" abstract="false" name="IncreaseInSharesReservedForIssuanceMaximumSharesToBeIssuedUponExerciseOfStockOptions" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_FacilityOneWalthamMassachusettsMember" abstract="true" name="FacilityOneWalthamMassachusettsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_DebtInstrumentFeeDueUponMaturityAccelerationPrepaymentTerminationPercentage" abstract="false" name="DebtInstrumentFeeDueUponMaturityAccelerationPrepaymentTerminationPercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_ContractWithCustomerRebatesWholesalerAndGPOFeesMember" abstract="true" name="ContractWithCustomerRebatesWholesalerAndGPOFeesMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_IncreaseDecreaseInUnbilledRevenue" abstract="false" name="IncreaseDecreaseInUnbilledRevenue" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ContractWithCustomerGrossToNetSalesAccrualRollForward" abstract="true" name="ContractWithCustomerGrossToNetSalesAccrualRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_EffectiveIncomeTaxRateReconciliationTaxExpenseBenefitExecutiveCompensationDisallowedIRCSec162mPercent" abstract="false" name="EffectiveIncomeTaxRateReconciliationTaxExpenseBenefitExecutiveCompensationDisallowedIRCSec162mPercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_RevenueRemainingPerformanceObligationVariableConsiderationAmount" abstract="false" name="RevenueRemainingPerformanceObligationVariableConsiderationAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ProductIBSRELAMember" abstract="true" name="ProductIBSRELAMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDueToCanceledInPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantIncreaseDueToCanceledInPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <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_ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesUnderEmployeeStockPurchasePlan" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardMaximumNumberOfSharesUnderEmployeeStockPurchasePlan" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_AccruedPaymentsDueToRelatedParty" abstract="false" name="AccruedPaymentsDueToRelatedParty" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_CollaborationPartnershipConcentrationRiskMember" abstract="true" name="CollaborationPartnershipConcentrationRiskMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_LesseeOperatingLeaseNumberOfRenewalOptions" abstract="false" name="LesseeOperatingLeaseNumberOfRenewalOptions" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="ardx_EmployeeStockPurchasePlanSharesPurchasedRollForward" abstract="true" name="EmployeeStockPurchasePlanSharesPurchasedRollForward" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_CollaborativeDevelopmentMember" abstract="true" name="CollaborativeDevelopmentMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_CollaborativeArrangementPotentialPaymentPerTerminationAgreementMaximum" abstract="false" name="CollaborativeArrangementPotentialPaymentPerTerminationAgreementMaximum" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ContractWithCustomerGrossToCreditsOrDeductionsIssued" abstract="false" name="ContractWithCustomerGrossToCreditsOrDeductionsIssued" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ThresholdPercentageOfSalesForTieredRoyalties" abstract="false" name="ThresholdPercentageOfSalesForTieredRoyalties" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityIncreaseDueToUnbilledPrepaymentsRecorded" abstract="false" name="ContractWithCustomerLiabilityIncreaseDueToUnbilledPrepaymentsRecorded" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_DebtInstrumentClosingFeeAmount" abstract="false" name="DebtInstrumentClosingFeeAmount" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_HealthCareRoyaltyPartnersIVLPMember" abstract="true" name="HealthCareRoyaltyPartnersIVLPMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_CommonStockSubjectToIssuedInducementGrantsShares" abstract="false" name="CommonStockSubjectToIssuedInducementGrantsShares" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <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_MaximumAggregateOfferingPrice" abstract="false" name="MaximumAggregateOfferingPrice" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_ContractWithCustomerProductSalesGrossToNetAccruals" abstract="false" name="ContractWithCustomerProductSalesGrossToNetAccruals" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_GrossToNetSalesAccrualAndReserveClassificationAxis" abstract="true" name="GrossToNetSalesAccrualAndReserveClassificationAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="ardx_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantDecreaseDueToStockIssuedForServicesInPeriod" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantDecreaseDueToStockIssuedForServicesInPeriod" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
  <xs:element id="ardx_CardinalHealthMember" abstract="true" name="CardinalHealthMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_FacilityTwoWalthamMassachusettsMember" abstract="true" name="FacilityTwoWalthamMassachusettsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_IncomeTaxDisclosureTable" abstract="true" name="IncomeTaxDisclosureTable" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:hypercubeItem" type="xbrli:stringItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityAmortizationEffectiveInterestRatePercent" abstract="false" name="ContractWithCustomerLiabilityAmortizationEffectiveInterestRatePercent" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_TwoThousandEightStockIncentivePlanMember" abstract="true" name="TwoThousandEightStockIncentivePlanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_TermLoan2022BMember" abstract="true" name="TermLoan2022BMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_StrezsakVersusArdelyxIncMember" abstract="true" name="StrezsakVersusArdelyxIncMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_CashCashEquivalentsAndInvestmentsGrossUnrealizedLosses" abstract="false" name="CashCashEquivalentsAndInvestmentsGrossUnrealizedLosses" nillable="true" xbrli:periodType="instant" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_StockOptionsAggregateIntrinsicValueAbstract" abstract="true" name="StockOptionsAggregateIntrinsicValueAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <xs:element id="ardx_ScheduleOfAdditionalDetailsOfLeasesTableTextBlock" abstract="false" name="ScheduleOfAdditionalDetailsOfLeasesTableTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityRevenueInvoicedButCashNotReceived" abstract="false" name="ContractWithCustomerLiabilityRevenueInvoicedButCashNotReceived" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_PerformanceBasedRestrictedStockUnitsMember" abstract="true" name="PerformanceBasedRestrictedStockUnitsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_CollaborationAndLicensingAgreementsNumberOfAmendments" abstract="false" name="CollaborationAndLicensingAgreementsNumberOfAmendments" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="ardx_AmerisourceBergenDrugCorporationMember" abstract="true" name="AmerisourceBergenDrugCorporationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityDecreaseInRevenueToBeRecognizedInNextTwelveMonths" abstract="false" name="ContractWithCustomerLiabilityDecreaseInRevenueToBeRecognizedInNextTwelveMonths" nillable="true" xbrli:periodType="duration" xbrli:balance="debit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_TermLoan2018Member" abstract="true" name="TermLoan2018Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_CollaborationAndLicensingAgreementsAbstract" abstract="true" name="CollaborationAndLicensingAgreementsAbstract" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:stringItemType"/>
  <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_ProductSupplyRevenueMember" abstract="true" name="ProductSupplyRevenueMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ShareBasedCompensationArrangementByShareBasedPaymentAwardEmployeeStockPurchasePlanGrossProceeds" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEmployeeStockPurchasePlanGrossProceeds" nillable="true" xbrli:periodType="duration" 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_CashCashEquivalentsAndInvestmentsGrossUnrealizedGains" abstract="false" name="CashCashEquivalentsAndInvestmentsGrossUnrealizedGains" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_NumberOfOperatingLeaseArrangements" abstract="false" name="NumberOfOperatingLeaseArrangements" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="xbrli:integerItemType"/>
  <xs:element id="ardx_LicenseAgreementDevelopmentCommercializationDistributionInJapanMember" abstract="true" name="LicenseAgreementDevelopmentCommercializationDistributionInJapanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_AccruedContractManufacturingCosts" abstract="false" name="AccruedContractManufacturingCosts" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_NonCashInterestExpenseOnDeferredRoyaltyObligationPolicyTextBlock" abstract="false" name="NonCashInterestExpenseOnDeferredRoyaltyObligationPolicyTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="ardx_IncreaseInSharesReservedForIssuanceOptionForAnnualIncreaseAsPercentageOfSharesOutstanding" abstract="false" name="IncreaseInSharesReservedForIssuanceOptionForAnnualIncreaseAsPercentageOfSharesOutstanding" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_GeographicInformationAndConcentrationsTextBlock" abstract="false" name="GeographicInformationAndConcentrationsTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityIncreasesToAmountsInvoicedButCashNotReceived" abstract="false" name="ContractWithCustomerLiabilityIncreasesToAmountsInvoicedButCashNotReceived" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_TermBLoanMember" abstract="true" name="TermBLoanMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_DerivativeIssued" abstract="false" name="DerivativeIssued" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_McKessonCorporationMember" abstract="true" name="McKessonCorporationMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_AccruedSalesAndMarketingExpenses" abstract="false" name="AccruedSalesAndMarketingExpenses" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_CollaborationAndLicensingAgreementsUpfrontLicenseFeesFirstInstallment" abstract="false" name="CollaborationAndLicensingAgreementsUpfrontLicenseFeesFirstInstallment" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_AstrazenecaMember" abstract="true" name="AstrazenecaMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ContractWithCustomerLiabilityRevenueToBeRecognizedInNextTwelveMonths" abstract="false" name="ContractWithCustomerLiabilityRevenueToBeRecognizedInNextTwelveMonths" nillable="true" xbrli:periodType="duration" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LeaseArrangementsDomain" abstract="true" name="LeaseArrangementsDomain" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_ShortTermInvestmentsPolicyTextBlock" abstract="false" name="ShortTermInvestmentsPolicyTextBlock" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:textBlockItemType"/>
  <xs:element id="ardx_ResearchCollaborationAndOptionAgreementMember" abstract="true" name="ResearchCollaborationAndOptionAgreementMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_TermLoan2022Member" abstract="true" name="TermLoan2022Member" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_AccountsReceivableCollaboratorMember" abstract="true" name="AccountsReceivableCollaboratorMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_SaleOfStockWeightedAveragePricePerShare" abstract="false" name="SaleOfStockWeightedAveragePricePerShare" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:perShareItemType"/>
  <xs:element id="ardx_ContractWithCustomerGrossToNetSalesAccruals" abstract="false" name="ContractWithCustomerGrossToNetSalesAccruals" nillable="true" xbrli:periodType="instant" xbrli:balance="credit" substitutionGroup="xbrli:item" type="xbrli:monetaryItemType"/>
  <xs:element id="ardx_LeaseArrangementsAxis" abstract="true" name="LeaseArrangementsAxis" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrldt:dimensionItem" type="xbrli:stringItemType"/>
  <xs:element id="ardx_CorporateBondsMember" abstract="true" name="CorporateBondsMember" nillable="true" xbrli:periodType="duration" substitutionGroup="xbrli:item" type="dtr-types:domainItemType"/>
  <xs:element id="ardx_DebtInstrumentPrepaymentFeePercentage" abstract="false" name="DebtInstrumentPrepaymentFeePercentage" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="dtr-types:percentItemType"/>
  <xs:element id="ardx_ShareBasedCompensationArrangementByShareBasedPaymentAwardEmployeesStockPurchasePlanPurchasedNumber" abstract="false" name="ShareBasedCompensationArrangementByShareBasedPaymentAwardEmployeesStockPurchasePlanPurchasedNumber" nillable="true" xbrli:periodType="instant" substitutionGroup="xbrli:item" type="xbrli:sharesItemType"/>
</xs:schema>
