Evaluation of CYP2C19, P2Y12, and ABCB1 polymorphisms and phenotypic response to clopidogrel in healthy Indian adults

INTRODUCTION: CYP2C19 and P2Y12 polymorphisms have been claimed to alter the pharmacodynamic response to clopidogrel. ABCB1 polymorphism has been associated with the efflux of clopidogrel resulting in decreased bioavailability. Due to paucity of data from Indian population, the present study was undertaken to evaluate the association of genetic polymorphisms of CYP2C19, P2Y12, and ABCB1 with inhibition of platelet aggregation (IPA) by clopidogrel. METHODS: Healthy adults (n = 90) of either gender were administered single dose of 300 mg clopidogrel. Baseline, 4 h postdose, and day 7 assessment of platelet aggregation and genotype of CYP2C19, P2Y12, and ABCB1 were carried out using standardized laboratory methods. The difference in the maximum platelet aggregation (MPA) between baseline and 4 h postdose was considered as delta-MPA (DMPA), and percentage change of MPA at 4 h from baseline was considered as IPA. Those with an IPA of <30% were considered as poor responders. Inferential statistics was applied to find out significant difference of these parameters between various groups of genetic polymorphisms. RESULTS: Mean (standard deviation [SD]) of MPA (%) at baseline, 4 h postdose, and day 7 were 78 (5), 56 (16), and 71 (8), respectively. Similarly, mean (SD) of DMPA (%) and IPA (%) were 23 (17) and 29 (21), respectively. A total of 54/90 (60%) cases were found to be poor responders to clopidogrel. A wild genotype (*1/*1) of CYP2C19 was observed in 35 (40.2%), 42 (48.3%) had *1/*2, 2 (2.3%) individuals had *1/*3, and 8 (9.2%) had *2/*2 mutant genotypes. Although statistically not significant (P = 0.09), a trend was observed in having decreased inhibition values (both MPA and IPA) as we proceed from wild genotype (*1/*1) to mutant genotypes in the order of *1/*2, *1/*3, and *2/*2. Similarly, in P2Y12, a wild haplotype (H1/H1) was present in 77 (89.5%) and 9 (10.5%) individuals had H1/H2 type. A statistically significant difference in DMPA and IPA was observed with more IPA by clopidogrel in individuals with H2 haplotype. No association was observed between the carriers and noncarriers of mutant (T) allele of ABCB1. CONCLUSION: A trend of decrease in the IPA with CYP2C19 genotypes and an increase in the same with the H2 haplotype of P2Y12 following clopidogrel in Indian healthy adults were observed. Assessment of genetic polymorphisms of the same may aid in personalizing the therapy with clopidogrel.