Prevalence of CYP2C9 and CYP2C19 variants and the impact on clopidogrel efficacy in patients having CYPC19*2 variant

Human cytochrome p450 enzymes play an important role in the metabolism of various substances. The CYP2C subfamily consists of various important drug-metabolizing enzymes such as CYP2C9 and CYP2C19. The objectives of the study include the determination of the frequency of genetic variants (CYP2C9*2, CYP2C9*3, and CYP2C19*2) of selected enzymes using allele-specific polymerase chain reaction (ASPCR) and its comparison with Indian as well as global past frequencies. We also aimed to study the impact of genetic mutation on clopidogrel efficacy and compare the efficacies between patients with and without CYP2C19*2 genetic variant.

In this study, the prevalence of variants CYP2C19*2, CYP2C9*2, and CYP2C9*3, the most popular variants of the respective enzymes, was determined using the ASPCR method. The correlation between the CYP2C19*2 variant and the antiplatelet activity of clopidogrel was studied using platelet aggregation assay (PAA).

The determined frequencies of CYP2C19*2, CYP2C9*2, and CYP2C9*3 are 46%, 9%, and 12%. These frequencies are indicative of homozygous as well as heterozygous mutations. Reduced clopidogrel efficacy was observed in patients with a heterozygous mutation of CYP2C19*2 variant.

The observed frequencies are not significantly different from that observed in earlier reported studies conducted across India and the world. Antiplatelet activity, as measured using the PAA method, was significantly lesser in patients having the CYP2C19*2 variant. The therapy failure in these patients can lead to serious cardiovascular consequences, and we propose determining the presence of the CYP2C19*2 variant before initiation of clopidogrel therapy.