CYP2C19 genotype-guided antiplatelet therapy in a patient with clopidogrel resistance

Abstract

We report a switch in antiplatelet medication based on platelet function and CYP2C19 genotype test results in a 74-year-old man with severe coronary arterial disease. Upon bare metal stent implantation at age 66, clopidogrel therapy (75 mg/ day) was initiated to supplement aspirin. Over the next eight years, the patient required multiple percutaneous coronary interventions for de novo coronary stenosis and in-stent restenosis. Platelet reactivity measured while on clopidogrel therapy was high, consistent with clopidogrel resistance. CYP2C19 genotype testing then revealed homozygosity for the *2 null allele. The *2/*2 designation indicates poor metabolizer status, indicating deficient capacity of the cytochrome p450 2C19 enzyme for activation of clopidogrel. A medication switch to prasugrel,which does not rely on activation by the 2C19 enzyme, reduced platelet reactivity by 86%. The patient has suffered no cardiovascular events in the 18 months since initiation of prasugrel therapy.