Abstract: AimTo investigate the variation of CYP2C9 isoenzyme activity in the microbial model in response to inhibitors of CYP2C9. MethodsUsing C.blakesleeana AS 3.910 as a model strain, the impact of CYP2C9 inhibitors on the metabolites yields of CYP2C9 substrates was determined and the drug-drug interactions among CYP2C9 substrates were evaluated. Liquid chromatography-mass spectrometry was used to analyze biotransformation products. ResultsBenzbromarone decreased the yield of 4′-hydroxytolbutamide from 100% to 14.5%; sulfaphenazole decreased the yield of O-demethylindomethacin from 75.2% to 9.9%; valproic acid decreased the yield of 4′-hydroxydiclofenac from 98.6% to 2.7%, separately. Tolbutamide, indomethacin and diclofenac interacted with each other, resulting in the decreased formation of metabolites catalyzed by CYP2C9. ConclusionThree CYP2C9 inhibitors inhibit the activity of CYP2C9 isoenzyme in C.blakesleeana AS 3.910 differently, and there are drug-drug interactions among CYP2C9 substrates.