Clopidogrel has anti-platelet activity by irreversible inhibition of the P2Y12 platelet receptor. Clopidogrel must be converted into an active metabolite in order to show anti-platelet activity. Hepatic CYP2C19 enzyme is one of the key hepatic enzymes which convert clopidogrel into active metabolite and its genetic polymorphism is related to clopidogrel resistance. CYP2C19 poor or intermediate metabolizer groups show reduced anti-platelet activity of clopidogrel compared to extensive metabolizer group.