Effects of CYP4F2 Polymorphism on Response to Warfarin During Induction Phase: A Prospective, Open-Label, Observational Cohort Study

Background: The cytochrome P450 (CYP) 4F2 isozyme has been reported to metabolize vitamin K ₁ in vitro, and the V433M polymorphism in the CYP4F2 gene has been associated with reduced vitamin K ₁ metabolism and the need for a higher maintenance dosage in patients receiving warfarin. Objective: The purpose of the present study was to evaluate the effects of . V433M polymorphism on warfarin response during the induction phase. Methods: Warfarin-naive white patients in whom warfarin was scheduled to be initiated with a target INR of 2 to 3 were enrolled into the study. On enrollment, a single blood sample for the genotyping of . CYP4F2, . CYP2C9, and . VKORC1 was drawn. The international normalized ratio (INR) was followed daily during induction and twice weekly until stable anticoagulation was reached. The relationships between several markers of warfarin response during induction and . CYP4F2 polymorphism were determined. Results: The cohort consisted of 241 patients (115 men; mean [SD] age, 55.2 [19.4] years; weight, 79.5 [18.3] kg). Most of the patients were carriers of the . CYP4F2 CC genotype (112 patients) or the . CT genotype (104 patients). In carriers of the . TT genotype (25 patients), INR >3 was >4-fold lower compared with that in carriers of the . CC or . CT genotype, suggesting that patients with the . TT genotype were less sensitive to warfarin during induction. Also in . TT carriers, the extent of excessive anticoagulation was >10-fold lower than in the other carriers. Both of these findings had a nominal . P value of <0.05. After adjustment for false discovery rate, none of the findings remained significant at a threshold . q value of <0.05. Among . CC carriers, the concurrent use of a statin was associated with a 1-mg/d reduction in warfarin maintenance dosage. No similar effect was noted in the . CT or . TT carriers, suggesting a possible genetic influence on warfarin-statin interaction. Conclusions: These preliminary findings suggest that among white patients treated with warfarin, . CYP4F2 polymorphism had a measurable effect on warfarin responsiveness during induction; however, the observed differences failed to reach the level of statistical significance. The possibility that the effect of statins on warfarin anticoagulation varies among carriers of different . CYP4F2 genotypes could not be excluded and should be evaluated further in a larger patient sample.