Impact of CYP3A4*1G Allele on Clinical Pharmacokinetics and Pharmacodynamics of Clopidogrel

Background and Objectives Resistance to the antiplatelet treatment with clopidogrel has both genetic and non-genetic causes. Polymorphic variants of cytochrome P450 3A4 isoenzyme involved in the bioactivation of clopidogrel might have an influence on responsiveness to the drug. The aim of this study was to evaluate the influence of CYP3A4*1G (IVS10? 12G > A, rs2242480) on the pharmacokinetics and pharmacodynamics of clopidogrel. Methods CYP3A4*1G polymorphism was determined in a group of 82 patients undergoing percutaneous coronary intervention and taking 75 mg of clopidogrel daily. Concentrations of clopidogrel and its metabolites, inactive carboxylic acid derivative and two diastereoisomers of active thiol metabolite: H3 and H4, were determined by a validated HPLC-MS/MS method. Pharmacodynamic effect was measured by an impedance method with a Multiplate analyzer. Moreover, an effect of factors, such as CYP2C19 phenotype, age, gender, body mass index and interactions with drugs metabolized by CYP3A4 were also investigated. Results In the studied group allele frequencies were: wt-0.921, *1G-0.079. Pharmacokinetic parameters of clopidogrel and its metabolites were not significantly different in carriers of *1G allele, comparing to wt/wt homozygotes. Platelet aggregation was higher in heterozygotes than in wt/wt carriers; however, the difference was not statistically significant (p = 0.484). In a multivariate analysis, which included age, body mass index, co-morbidities and coadministered drugs, CYP3A4*1G was not a predictor of values of H3 and H4 pharmacokinetic parameters and platelet aggregation. Conclusion CYP3A4*1G might not be a significant contributor to the variability in pharmacokinetic and pharmacodynamic response to clopidogrel therapy.