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On-treatment platelet reactivity to clopidogrel is variable and in part genetic dependent. In African American (AA) patients, the relation between on-treatment platelet reactivity to clopidogrel and the factors that influence this interaction is unknown. The present study aims to evaluate on-treatment platelet reactivity to clopidogrel in AA patients and its interaction to race and CYP2C19*2 loss of function mutation.The study cohort included 289 consecutive patients presenting for percutaneous coronary intervention who were entered into a prospective observational registry. High on-treatment platelet reactivity (HTPR) was defined as P2Y12 reaction units (PRU) ≥208 with VerifyNow P2Y12 assay and >50% by vasodilator-stimulated phosphoprotein phosphorylation assay platelet reactivity index (VASP PRI) measured 6 to 24 hours postprocedure. CYP2C19*2 (rs4244285) genotype was analyzed by real-time polymerase chain reaction.The prevalence of HTPR by both PRU (56% vs 35%, P = .003) and VASP PRI (67% vs 45%, P = .002) is more common in AAs compared with whites, respectively. African American patients had higher on-treatment mean PRU (207 ± 110 vs 160 ± 102, P = .002) and VASP PRI (49 ± 26 vs 38 ± 26, P = .004). African Americans also had a higher prevalence of CYP2C19*2 allele carrier status compared with whites (43% vs 29%, P = .04). African American race (P = .008) and CYP2C19*2 allele status (P = .02) independently had significant effects on PRU and VASP. Multivariable logistic regression analysis has shown that both CYP2C19*2 allele carrier status and AA race were independent correlates of HTPR for PRU ≥208.African American patients undergoing percutaneous coronary intervention not only have a higher prevalence of HTPR to clopidogrel but also have higher CYP2C19*2 allele carrier status compared with whites. Careful selection of antiplatelet agents should be considered in an AA population at higher risk for ischemic complications.