Study on the Effect of Three CYP2C9 Variants on Drug–Drug Interaction Related to Six Drugs In Vitro by LC–MS/MS Method

The influence of genetic polymorphism of metabolic enzymes on drug–drug interactions (DDI) should be thoroughly investigated owing to its remarkable effect on therapeutic treatments that are futile. Here, different from earlier articles focused on various CYP subfamilies and their isoforms, the effect of genetic polymorphs of a particular isoform, CYP2C9, was comprehensively studied. Using diclofenac as probe substrate, the influence of three CYP2C9 variants (CYP2C9*1, *2 and *3) on DDI was conducted from the measurement of inhibitory ability of six drugs towards three variants. A modified LC–MS/MS method according to former report was constructed for the determination of 4ʹ-hydroxydiclofenac in CYP2C9 enzyme incubation system and validated for accuracy, precision, linearity range within the acceptance criteria for regulatory guidelines. After selecting appropriate incubation time and enzyme concentration, the kinetic parameters of three CYP2C9 variants towards diclofenac were examined and half inhibitory concentrations (IC 50 ) of six drugs towards three CYP2C9 variants were determined. IC 50 of paroxetine and losartan towards CYP2C9*2 were almost threefold higher and 2.5-fold lower than that towards CYP2C9*1, respectively. IC 50 of glibenclamide towards CYP2C9*3 was twofold more than that towards CYP2C9*1. Our results could offer effective guidelines for co-administration of these six drugs with various CYP2C9 substrates in individuals carrying variant CYP2C9 alleles, also broaden the application area of LC–MS/MS.