OBJECTIVETo investigate the impact of omeprazole on platelet response to clopidogrel and the effect of polymorphisms of CYP2C19 on the antiplatelet effect of clopidogrel.

METHODSPlatelet aggregation (PA) was assessed before 300 mg aspirin plus 300 mg loading dose of clopidogrel and after 300 mg aspirin plus 75 mg maintenance dose of clopidogrel 7 days later in 414 patients with acute coronary syndrome who have undergone percutaneous coronary intervention (PCI). Thereafter, gastric mucosal protective drugs were given (omeprazolem 20 mg, n=224 or cimetidine 800 mg, n=190). Fourteen days later, PA was measured again. Genotypes of CYP2C19*2 were analyzed with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP).

RESULTSAfter taken aspirin and clopidogrel, PA has decreased significantly in both groups. Compared with cimetidine, omeprazole had no significant impact on PA on 7 and 21 days post PCI. Compared with homozygotes or heterozygotes for the wild-type CYP2C19*2, patients with CYP2C19*2 AA genotype had significantly higher PA on 7 and 21 days post PCI (P<0.05).

CONCLUSIONNo attenuating effect on platelet response to clopidogrel has been observed for Omeprazole. The variant of CYP2C19*2 AA genotype is significantly associated with attenuated response to clopidogrel.