EMEA基因毒性杂质限度指南

CompanyDocumentnumber：WTUT-WT88Y-W8BBGB-BWYTT-19998EMEA基因毒性杂质限度指南基因毒性杂质限度指南（中英文对照）London,28June2006CPMP/SWP/5199/02EMEA/CHMP/QWP/251344/2006TheEuropeanAgencyfortheEvaluationofMedicinalProducts欧洲共同体药物评审委员会(EMEA)COMMITTEEFORMEDICINALPRODUCTSFORHUMANUSE人用药品委员会(CHMP)GUIDLINEONTHELIMITSOFGENOTOXICIMPURITIES基因毒性杂质限度指南DESCUSSIONINTHESAFETYWORKINGPARTY安全工作组之内的讨论June2002-October2002TRANSMISSIONTOCPMPCPMP传递December2002RELEASEFORCONSULTATION专家讨论December2002DEADLINEFORCOMMENTS建议收集最后期限March2003DISCUSSIONINTHESAFETYWORKINGPARTYANDQUALITYWORKINGPARTY安全工作组和质量工作组之间的讨论June2003-February2004TRANSMISSIONTOCPMP转移给CPMPMarch2004RE-RELEASEFORCONSULTATION再次放行给顾问团June2004DEADLINEFORCOMMENTS收集意见的最后期限December2004DISCUSSIONINTHESAFETYWORKINGPARTYANDQUALITYWORKINGPARTY安全工作组和质量工作组之间的讨论February2005-May2006ADOPTIONBYCHMP被CHMP采用28June2006DATEFORCOMINGINTOEFFECT生效日期01January2007KEYWORDS关键词Impurities;Genotoxicity;Thresholdoftoxicologicalconcern(TTC);Structureactivityrelationship(SAR)GUIDLINEONTHELIMITSOFGENOTOXICIMPURITIES基因毒性杂质限度指南TABLEOFCONTENTS目录EXECUTIVESUMMARY内容摘要..............................................................................................31.INTRODUCTION介绍...............................................................................................................32.SCOPE范围...............................................................................................................................33.LEGALBASIS法律依据............................................................................................................34.TOXICOLOGICALBACKGROUND毒理学背景....................................................................45.RECOMMENDATIONS建议.....................................................................................................4GenotoxicCompoundsWithSufficientEvidenceforaThreshold-RelatedMechanism具有充分证据证明其阈值相关机理的基因毒性化合物.........................................................4GenotoxicCompoundsWithoutSufficientEvidenceforaThreshold-RelatedMechanism不具备充分证据支持其阈值相关机理的基因毒性化合物......................................................5PharmaceuticalAssessment药学..................................................................................5ToxicologicalAssessment毒理学评价...................................................................................5ApplicationofaThresholdofToxicologicalConcern毒理学担忧阈值应用........................5DecisionTreeforAssessmentofAcceptabilityofGenotoxicImpurities基因毒性杂质可接受性评价决策树..........................................................................................7REFERENCES.参考文献................................................................................................................8EXECUTIVESUMMARY内容摘要ThetoxicologicalassessmentofgenotoxicimpuritiesandthedeterminationofacceptablelimitsforsuchimpuritiesinactivesubstancesisadifficultissueandnotaddressedinsufficientdetailintheexistingICHQ3Xguidances.Thedatasetusuallyavailableforgenotoxicimpuritiesisquitevariableandisthemainfactorthatdictatestheprocessusedfortheassessmentofacceptablelimits.Intheabsenceofdatausuallyneededfortheapplicationofoneoftheestablishedriskassessmentmethods,.datafromcarcinogenicitylong-termstudiesordataprovidingevidenceforathresholdmechanismofgenotoxicity,implementationofagenerallyapplicableapproachasdefinedbytheThresholdofToxicologicalConcern(TTC)isproposed.ATTCvalueofμg/dayintakeofagenotoxicimpurityisconsideredtobeassociatedwithanacceptablerisk(excesscancerriskof<1in100,000overalifetime)formostpharmaceuticals.Fromthisthresholdvalue,apermittedlevelintheactivesubstancecanbecalculatedbasedontheexpecteddailydose.Higherlimitsmaybejustifiedundercertainconditionssuchasshort-termexposureperiods.基因毒性杂质的毒理学评估和这些杂质在活性药物中的可接受的测定是一件困难的事情，并且在现有的ICHQ3X指南中也没有详细的规定。现有的关于基因毒性杂质的相关数据是容易变化的，也是对杂质可接受标准如何进行评价的主要影响因素。如果缺少风险评估方法所需要的数据，比如，致癌作用的长期研究数据，或为基因毒性的阀值提供证据的数据，一般建议使用一般通用的被定义为毒理学关注的阈值（TTC）的方法。一个“μg/day”的TTC值，即相当于每天摄入μg的基因毒性杂质，被认为对于大多数药品来说是可以接受的风险（一生中致癌的风险小于十万分之1）。按照这个阀值，可以根据这个预期的每日摄入量计算出活性药物中可接受的杂质水平。较高的临界值可以在特定的条件下，如短期暴露周期等，进行推算。1.INTRODUCTION介绍Ageneralconceptofqualificationofimpuritiesisdescribedintheguidelinesforactivesubstances(Q3A,ImpuritiesinNewActiveSubstances)ormedicinalproducts(Q3B,ImpuritiesinNewMedicinalProducts),wherebyqualificationisdefinedastheprocessofacquiringandevaluatingdatathatestablishesthebiologicalsafetyofanindividualimpurityoragivenimpurityprofileatthelevel(s)specified.Inthecaseofimpuritieswithagenotoxicpotential,determinationofacceptabledoselevelsisgenerallyconsideredasaparticularlycriticalissue,whichisnotspecificallycoveredbytheexistingguidelines.在原料药（Q3A）和药物制剂（Q3B）的杂质指导原则中，杂质限度确定的依据包括各个杂质的生物安全性数据或杂质在某特定含量水平的研究概况。而对于遗传毒性杂质限度的确定，通常都认为是特别关键的问，但目前尚无相关的指导原则。2.SCOPE范围ThisGuidelinedescribesageneralframeworkandpracticalapproachesonhowtodealwithgenotoxicimpuritiesinnewactivesubstances.Italsorelatestonewapplicationsforexistingactivesubstances,whereassessmentoftherouteofsynthesis,processcontrolandimpurityprofiledoesnotprovidereasonableassurancethatnoneworhigherlevelsofgenotoxicimpuritiesareintroducedascomparedtoproductscurrentlyauthorisedintheEUcontainingthesameactivesubstance.ThesamealsoappliestovariationstoexistingMarketingAuthorisationspertainingtothesynthesis.Theguidelinedoes,however,notneedtobeappliedretrospectivelytoauthorisedproductsunlessthereisaspecificcauseforconcern.本指导原则阐述了如何处理新原料药中遗传毒性杂质的一般框架和实际方法。该指导原则也适用于已有原料药的新申请，如果其合成路线、过程控制和杂质研究尚无法确保不会产生新的或更高含量的遗传毒性杂质（与EU目前批准的相同原料药相比）。该指导原则同样适用于已上市原料药有关合成方面的补充申请。除非有特殊原因，本指导原则不适用于已上市的产品。Inthecurrentcontexttheclassificationofacompound(impurity)asgenotoxicingeneralmeansthattherearepositivefindingsinestablishedinvitroorinvivogenotoxicitytestswiththemainfocusonDNAreactivesubstancesthathaveapotentialfordirectDNAdamage.Isolatedinvitrofindingsmaybeassessedforinvivorelevanceinadequatefollow-uptesting.Intheabsenceofsuchinformationinvitrogenotoxicantsareusuallyconsideredaspresumptiveinvivomutagensandcarcinogens.目前对于基因毒性杂质的分类主要是指：在以DNA反应物质为主要研究对象的体内体外试验中，如果发现它们对DNA有潜在的破坏性，那可称之为基因毒性。如果有足够的后续试验，可由单独的体外试验结果，对它的体内关联性进行评估。在缺乏这样的信息时，体外基因毒性物质经常被考虑为假定的体内诱变剂和致癌剂。3.LEGALBASIS法规依据ThisguidelinehastobereadinconjunctionwithDirective2001/83/EC(asamended)andallrelevantCHMPGuidancedocumentswithspecialemphasison:在阅读该指南时有必要参考“Directive2001/83/EC”以及相关的CHMP指南文件，特别是以下几个指南：ImpuritiesTestingGuideline:ImpuritiesinNewDrugSubstances(CPMP/ICH/2737/99,ICHQ3A(R))NoteforGuidanceonImpuritiesinNewDrugProducts(CPMP/ICH/2738/99,ICHQ3B(R))NoteforGuidanceonImpurities:ResidualSolvents(CPMP/ICH/283/95)NoteforGuidanceonGenotoxicity:GuidanceonSpecificAspectsofRegulatoryGenotoxicityTestsforPharmaceuticals(CPMP/ICH/141/95,ICHS2A)NoteforGuidanceonGenotoxicity:AStandardBatteryforGenotoxicityTestingofPharmaceuticals(CPMP/ICH/174/95,ICHS2B)4.TOXICOLOGICALBACKGROUND毒理学背景Accordingtocurrentregulatorypracticeitisassumedthat(invivo)genotoxiccompoundshavethepotentialtodamageDNAatanylevelofexposureandthatsuchdamagemaylead/contributetotumourdevelopment.Thusforgenotoxiccarcinogensitisprudenttoassumethatthereisnodiscerniblethresholdandthatanylevelofexposurecarriesarisk.根据目前的研究实践，具有（体内）遗传毒性的化合物在任何暴露量下都有可能对DNA产生损伤，而这种损伤可能会引发肿瘤。因此，对于遗传毒性致癌物质，应谨慎认为不存在明确的阈值，任何暴露量下都存在风险。However,theexistenceofmechanismsleadingtobiologicallymeaningfulthresholdeffectsisincreasinglyacknowledgedalsoforgenotoxicevents.Thisholdstrueinparticularforcompoundsinteractingwithnon-DNAtargetsandalsoforpotentialmutagens,whicharerapidlydetoxifiedbeforecomingintocontactwithcriticaltargets.Theregulatoryapproachtosuchchemicalscanbebasedontheidentificationofacriticalno-observed-effectlevel(NOEL)anduseofuncertaintyfactors.然而，对于一些遗传毒性事件，其产生生物学意义的阈值效应的机理正越来越为人所了解。对于非DNA靶点的化合物和潜在致突变剂更是如此，因为它们在与关键靶点接触前就已经去毒化了。对于这些化合物，研究的基础可以是确定关键的未观察到影响的剂量（NOEL）和采用不确定因子。EvenforcompoundswhichareabletoreactwiththeDNAmolecule,extrapolationinalinearmannerfromeffectsinhigh-dosestudiestoverylowlevel(human)exposuremaynotbejustifiedduetoseveralprotectivemechanismsoperatingeffectivelyatlowdoses.However,atpresentitisextremelydifficulttoexperimentallyprovetheexistenceofthresholdforthegenotoxicityofagivenmutagen.Thus,intheabsenceofappropriateevidencesupportingtheexistenceofathresholdforagenotoxiccompoundmakingitdifficulttodefineasafedoseitisnecessarytoadoptaconceptofalevelofexposurethatcarriesanacceptablerisk.即使对能与DNA分子发生反应的化合物，由于低剂量时有多种有效的保护机制存在，而不能将高剂量下的影响以线性方式外推到很低的（人）暴露水平。不过，目前要用实验方法证明某诱变剂的遗传毒性阈值仍然非常困难。所以，在缺乏恰当的证据支持遗传毒性阈值存在的情况下，确定安全剂量很困难，因此非常有必要采用一个可接受风险的暴露水平概念。5.RECOMMENDATIONS建议AsstatedintheQ3Aguideline,actualandpotentialimpuritiesmostlikelytoariseduringsynthesis,purificationandstorageofthenewdrugsubstanceshouldbeidentified,basedonasoundscientificappraisalofthechemicalreactionsinvolvedinthesynthesis,impuritiesassociatedwithrawmaterialsthatcouldcontributetotheimpurityprofileofthenewdrugsubstance,andpossibledegradationproducts.Thisdiscussioncanbelimitedtothoseimpuritiesthatmightreasonablybeexpectedbasedonknowledgeofthechemicalreactionsandconditionsinvolved.Guidedbyexistinggenotoxicitydataorthepresenceofstructuralalerts,potentialgenotoxicimpuritiesshouldbeidentified.Whenapotentialimpuritycontainsstructuralalerts,additionalgenotoxicitytestingoftheimpurity,typicallyinabacterialreversemutationassay,shouldbeconsidered(Doboetal.2006,Mülleretal.2006).WhileaccordingtotheQ3Aguidelinesuchstudiescanusuallybeconductedonthedrugsubstancecontainingtheimpuritytobecontrolled,studiesusingisolatedimpuritiesaremuchmoreappropriateforthispurposeandhighlyrecommended.正如Q3A指导原则所述，根据合理的化学反应机理，在新的原料药合成、纯化和贮存过程中很有可能产生实际的和潜在的杂质。依据现有的“可能引起遗传毒性的结构”数据库，潜在的遗传毒性杂质应能被确认。如果潜在的杂质含有可引起遗传毒性的结构单元，该杂质应考虑进行遗传毒性试验（一般是细菌回复突变试验）（Dobo等，2006）。虽然Q3A指导原则认为这些研究采用含有那些需控制杂质的原料药进行是可行的，但用分离出来的杂质进行这些研究更恰当，也是高度推荐的方法。Fordeterminationofacceptablelevelsofexposuretogenotoxiccarcinogensconsiderationsofpossiblemechanismsofactionandofthedose-responserelationshipareimportantcomponents.Basedontheaboveconsiderationsgenotoxicimpuritiesmaybedistinguishedintothefollowingtwoclasses:根据以上论述，遗传毒性杂质可以归纳成以下两类：-Genotoxiccompoundswithsufficient(experimental)evidenceforathreshold-relatedmechanism有充分阈值相关机理证据（实验）的遗传毒性化合物-Genotoxiccompoundswithoutsufficient(experimental)evidenceforathreshold-relatedmechanism无充分阈值相关机理证据（实验）的遗传毒性化合物GenotoxicCompoundsWithSufficientEvidenceforaThreshold-RelatedMechanism具有充分证据证明其阈值相关机理的基因毒性化合物Examplesofmechanismsofgenotoxicitythatmaybedemonstratedtoleadtonon-linearorthresholdeddose-responserelationshipsincludeinteractionwiththespindleapparatusofcelldivisionleadingtoaneuploidy,topoisomeraseinhibition,inhibitionofDNAsynthesis,overloadingofdefencemechanisms,metabolicoverloadandphysiologicalperturbations.inductionoferythropoeisis,hyper-orhypothermia).非线性或阈值明确的剂量效应关系的遗传毒性机理包括：与细胞分化过程中纺锤体相互作用；拓扑异构酶抑制；DNA合成抑制；过度的防御机制；代谢过度和生理性干扰（如诱导红血球生成，高体温和低体温）。For(classesof)compoundswithclearevidenceforathresholdedgenotoxicity,exposurelevelswhicharewithoutappreciableriskofgenotoxicitycanbeestablishedaccordingtotheprocedureasoutlinedforclass2solventsintheQ3CNoteforGuidanceonImpurities:ResidualSolvents.Thisapproachcalculatesa“PermittedDailyExposure”(PDE),whichisderivedfromtheNOEL,orthelowestobservedeffectlevel(LOEL)inthemostrelevant(animal)studyusing“uncertaintyfactors”(UF).有明确遗传毒性阈值的化合物，不产生遗传毒性风险的暴露水平可以被确定，方法可参照Q3C“杂质指导原则”中二类溶剂的限度确定方法。该方法可计算“每日最大允许暴露量”（PDE），数据来源于“不确定因数”动物研究中的NOEL（未观察到效果的最低水平）或观察到效果的最低水平（LOEL）。GenotoxicCompoundsWithoutSufficientEvidenceforaThreshold-RelatedMechanism不具备充分证据支持其阈值相关机理的基因毒性化合物Theassessmentofacceptabilityofgenotoxicimpuritiesforwhichnothresholdmechanismsareidentifiedshouldincludebothpharmaceuticalandtoxicologicalevaluations.Ingeneral,pharmaceuticalmeasurementsshouldbeguidedbyapolicyofcontrollinglevelsto“aslowasreasonablypracticable”(ALARPprinciple),whereavoidingisnotpossible.LevelsconsideredbeingconsistentwiththeALARPprinciplefollowingpharmaceuticalassessmentshouldbeassessedforacceptabilityfromatoxicologicalpointofview(seedecisiontree&followingsections).对于此类遗传毒性杂质，研究应包括药学和毒理学评估。总之，如果杂质无法避免，药学方面的控制应遵循“合理可行的最低限量”原则（ALARP原则）。符合ALARP原则的杂质水平再经毒理学方面的进一步评估，以验证其合理性（见决策树和以下章节）。PharmaceuticalAssessment药学评价Aspecificdiscussion–aspartoftheoveralldiscussiononimpurities(seeQ3A(R))–shouldbeprovidedintheapplicationwithregardtoimpuritieswithpotentialgenotoxicity.申请材料应提供关于潜在遗传毒性杂质的特别讨论资料（见Q3A（R））。Arationaleoftheproposedformulation/manufacturingstrategyshouldbeprovidedbasedonavailableformulationoptionsandtechnologies.Theapplicantshouldhighlight,withinthechemicalprocessandimpurityprofileofactivesubstance,allchemicalsubstances,usedasreagentsorpresentasintermediates,orside-products,knownasgenotoxicand/orcarcinogenic.alkylatingagents).需要根据现在的配方选择和技术，提供证明所选的配方/生产策略合理性的证据。申请人应在合成工艺和杂质研究部分重点指出所有的化学物质，包括用到的试剂、中间体、副产物，哪些是已知遗传毒性和/或致癌性物质（如烷化剂）。Moregenerally,reactingsubstancesandsubstanceswhichshow“alertingstructure”intermsofgenotoxicitywhicharenotsharedwiththeactivesubstanceshouldbeconsidered(see.Doboetal.2006).Potentialalternativeswhichdonotleadtogenotoxicresiduesinthefinalproduct,shouldbeusedifavailable.值得关注的是，虽然有些含有“可能引起遗传毒性的结构”（alertingstructure）的反应试剂与最终活性物质并没有共同结构，但也要考虑它们的遗传毒性(see.Doboetal.2006).。如果有可能，应该对它们进行一些替代研究，以使最终产品中不会引入基因毒性残留。Ajustificationneedstobeprovidedthatnoviablealternativeexists,includingalternativeroutesofsynthesisorformulations,differentstartingmaterials.Thismightforinstanceincludecaseswherethestructure,whichisresponsibleforthegenotoxicand/orcarcinogenicpotentialisequivalenttothatneededinchemicalsynthesis.alkylationreactions).需要提供充分的论证来说明没有可行的替代方法存在，包括可替代的合成路线或配方，不同的起始物料等。比如，应证明具有遗传毒性和/或致癌性的结构在化学合成中（如烷化反应）是必需的。Ifagenotoxicimpurityisconsideredtobeunavoidableinadrugsubstance,technicalefforts.purificationsteps)shouldbeundertakentoreducethecontentofthegenotoxicresiduesinthefinalproductincompliancewithsafetyneedsortoalevelaslowasreasonablypracticable(seesafetyassessment).Dataonchemicalstabilityofreactiveintermediates,reactants,andothercomponentsshouldbeincludedinthisassessment.如果遗传毒性杂质在原料中不可避免，则应该采取适当的技术（如纯化步骤）降低该杂质的含量，以满足安全性要求，或符合“合理可行的最低限量”原则（见安全评估）。药学评估还应包括反应中间体、反应物和其它组件等的化学稳定性研究。Detectionand/orquantificationoftheseresiduesshouldbedonebystate-of-the-artanalyticaltechniques.应该使用比较先进的分析检测技术来检测和量化这些残留的杂质。ToxicologicalAssessment毒理学评价Theimpossibilityofdefiningasafeexposurelevel(zeroriskconcept)forgenotoxiccarcinogenswithoutathresholdandtherealizationthatcompleteeliminationofgenotoxicimpuritiesfromdrugsubstancesisoftenunachievable,requiresimplementationofaconceptofanacceptablerisklevel,.anestimateofdailyhumanexposureatandbelowwhichthereisanegligiblerisktohumanhealth.鉴于在没有明确阈值的前提下定义安全暴露水平（零风险）是不可能的，且从原料药中完全除去遗传毒性杂质经常是很难做到的，所以有必要提出一个“可接受风险水平”（acceptablerisklevel）的概念，比如估算一个“每日最大暴露量”值，低于该暴露量时就可以忽略其对人体健康的风险。ProceduresforthederivationofacceptablerisklevelsareconsideredintheAppendix3oftheQ3CNoteforGuidanceonImpurities:ResidualSolventsforClass1solvents.However,theseapproachesrequireavailabilityofadequatedatafromlong-termcarcinogenicitystudies.对于可接受风险水平的推导过程请参见Q3C（杂质指南注释:一类溶液残留）中的附件三。然而，应用这些方法必须有足够多的长期致癌性研究数据。Inmostcasesoftoxicologicalassessmentofgenotoxicimpuritiesonlylimiteddatafrominvitrostudieswiththeimpurity.Amestest,chromosomalaberrationtest)areavailableandthusestablishedapproachestodetermineacceptableintakelevelscannotbeapplied.Calculationof“safetymultiples”frominvitrodata.Amestest)areconsideredinappropriateforjustificationofacceptablelimits.Moreover,negativecarcinogenicityandgenotoxicitydatawiththedrugsubstancecontainingtheimpurityatlowppmlevelsdonotprovidesufficientassuranceforsettingacceptablelimitsfortheimpurityduetothelackofsensitivityofthistestingapproach.Evenpotentmutagensandcarcinogensaremostlikelytoremainundetectedwhentestedaspartofthedrugsubstance,.atverylowexposurelevels.Apragmaticapproachisthereforeneededwhichrecognisesthatthepresenceofverylowlevelsofgenotoxicimpuritiesisnotassociatedwithanunacceptablerisk.大多数情况下，遗传毒性杂质的毒理学评估只是局限于杂质的体外研究（如Ames试验，染色体畸变试验），但这些方法并不适用于确定杂质可接受的摄入水平。也就是说，根据体外数据（如Ames试验）计算杂质的“安全倍数（safetymultiples）”、进而确定可接受的限度，是不合适的。此外，用含有较低（ppm级）杂质水平的原料药研究其致癌性和遗传毒性，即使得出阴性结果也不足以确保该杂质限度的合理性，因为这种试验方法缺少必要的灵敏度。有些具有很强致突变性和致癌性物质与原料药一起进行试验时，因为在非常低的暴露水平情况下，很有可能因为低于检测限而无法检出。所以，如果认识到含量非常低的遗传毒性杂质不存在“不可接受的风险”（unacceptablerisk），那么可以采取实用的方法来控制该杂质。ApplicationofaThresholdofToxicologicalConcern毒理学相关的阈值应用Athresholdoftoxicologicalconcern(TTC)hasbeendevelopedtodefineacommonexposurelevelforanyunstudiedchemicalthatwillnotposeariskofsignificantcarcinogenicityorothertoxiceffects(Munroetal.1999,KroesandKozianowski2002).ThisTTCvaluewasestimatedtobeμg/person/day.TheTTC,originallydevelopedasa“thresholdofregulation”attheFDAforfoodcontactmaterials(Rulis1989,FDA1995)wasestablishedbasedontheanalysisof343carcinogensfromacarcinogenicpotencydatabase(Goldetal.1984)andwasrepeatedlyconfirmedbyevaluationsexpandingthedatabasetomorethan700carcinogens(Munro1990,Cheesemanetal.1999,Kroesetal.2004).Theprobabilitydistributionofcarcinogenicpotencieshasbeenusedtoderiveanestimateofadailyexposurelevel(μg/person)ofmostcarcinogenswhichwouldgiverisetolessthanaoneinamillion(1x10-6)upperboundlifetimeriskofcancer(“virtuallysafedose”).Furtheranalysisofsubsetsofhighpotencycarcinogensledtothesuggestionofa10-foldlowerTTCμg/day)forchemicalswithstructuralalertsthatraiseconcernforpotentialgenotoxicity(Kroesetal.2004).“毒理学关注的阈值”用于定义那些不会产生显着致癌性或其他毒性作用、但又未明确研究的化合物的“常见暴露量”（commonexposurelevel）(Munroetal.1999,KroesandKozianowski2002)。该TTC估计值是μg/人/日。TTC概念最早来源于FDA关于食品接触材料的“规定阈值”（athresholdofregulation）（Rulis1989,FDA1995），该阈值根据对致癌能力数据库(Goldetal.1984)中343种致癌物质的分析结果得出。随后该数据库扩大到700多个致癌性物质(Munro1990,Cheesemanetal.1999,Kroesetal.2004)，这种分析结果不断得到重复验证。通过对致癌能力的概率分布进行评价，可以得到一个对大多数致癌物质适用的“日常摄入水平(μg/person)”，此水平造成的一生中患癌症的风险小于正常风险水平的上限1x10-6（真实的安全剂量）。对于含有“可能引起遗传毒性结构”的化合物，其TTC应严格10倍（μg/日）（Kroesetal.2004）。However,forapplicationofaTTCintheassessmentofacceptablelimitsofgenotoxicimpuritiesindrugsubstancesavalueofμg/day,correspondingtoa10-5lifetimeriskofcancercanbejustifiedasforpharmaceuticalsabenefitexists.ItshouldberecognizedinthiscontextthatthemethodsonwhichtheTTCvalueisbased,aregenerallyconsideredveryconservativesincetheyinvolvedasimplelinearextrapolationfromthedosegivinga50%tumourincidence(TD50)toa1in106incidence,usingTD50dataforthemostsensitivespeciesandmostsensitivesite(several“worstcase”assumptions)(Munroetal.1999).然而，用TTC评估原料药中的遗传毒性杂质限度，μg/日（相当于10万分之一的患癌风险）是可以接受的。应该承认，基于TTC值控制遗传毒性杂质是非常保守的，因为这只是根据从产生50%肿瘤发生率（TD50）到百万分之一致癌率的剂量线性推导得到的，而且TD50数据是用最敏感的动物和最敏感的部位研究得到的（几个“最坏条件”假设）（Munroetal.1999）。SomestructuralgroupswereidentifiedtobeofsuchhighpotencythatintakesevenbelowtheTTCwouldbeassociatedwithahighprobabilityofasignificantcarcinogenicrisk(Cheesemanetal.1999,Kroesetal.2004).Thisgroupofhighpotencygenotoxiccarcinogenscomprisesaflatoxin-like-,nitroso-,andazoxy-compoundsthathavetobeexcludedfromtheTTCapproach.Riskassessmentofmembersofsuchgroupsrequirescompound-specifictoxicitydata.有几个结构基团被认定为具有非常高的基因毒性，它们即使被摄入低于TTC值的量也会面临非常高的基因毒性风险(Cheesemanetal.1999,Kroesetal.2004)。这些高致癌性物质包括黄曲霉素类、N-亚硝基物和偶氮类化合物，不适用TTC方法。这类化合物的风险评估需采用专门的毒性数据。TheremaybereasonstodeviatefromtheTTCvaluebasedontheprofileofgenotoxicityresults.根据基因杂质概况，有些情况下会偏离TTC值。PositiveresultfrominvitrostudiesonlymayallowtoexemptanimpurityfromlimitationatTTCleveliflackofinvivorelevanceofthefindingsisconvincinglydemonstratedbasedonaweight-ofevidenceapproach(seeICHS2guidelines).Thisapproachwillusuallyneednegativeresultswiththeimpurityfromsomeadditionalinvitroand/orappropriateinvivotesting.假如按照证据权衡法能充分证明“结果缺乏体内相关性”，体外试验的阳性结果也仅能在TTC水平上排除一个杂质(参见ICH指南S2)。这种方法经常需要在额外的体外试验和/或合理的体内试验，并且得到杂质的阴性结果。ATTCvaluehigherthanμg/daymaybeacceptableundercertainconditions,.short-termexposure,fortreatmentofalife-threateningcondition,whenlifeexpectancyislessthan5years,orwheretheimpurityisaknownsubstanceandhumanexposurewillbemuchgreaterfromothersources.food).Genotoxicimpuritiesthatarealsosignificantmetabolitesmaybeassessedbasedontheacceptabilityofthemetabolites.某些情况下TTC值高于μg/日也是可以接受的，如短期用药；用于治疗威胁生命疾病的药物；或人的存活期少于5年；或该杂质是已知物质，人体从其他途经（如食物）获得的暴露量远远高于药物途经。如果遗传毒性杂质本身就是重要的代谢物，那么该杂质可以根据代谢物的可接受限度进行控制。TheconcentrationlimitsinppmofgenotoxicimpurityindrugsubstancederivedfromtheTTCcanbecalculatedbasedontheexpecteddailydosetothepatientusingequation(1).采用下列，从TTC值和日服用剂量，可以计算出原料药中的基因毒性杂质的浓度限度。(1)Concentrationlimit(ppm)=TTC[μg/day]/dose(g/day]浓度限度（ppm）=TTC[μg/day]/剂量(g/day]TheTTCconceptshouldno