Clopidogrel Resistance in Japanese Patients Scheduled forPercutaneous Coronary Intervention

BACKGROUND: Dual antiplatelet therapy with acetylsalicylic acid (ASA) and a P2Y(12) ADP-receptor blocker is standard for prevention of coronary stent thrombosis. Clopidogrel, a 2(nd)-generation P2Y(12) blocker, has recently become available in Japan and this study aimed to evaluate its antiplatelet effects in Japanese patients. METHODS AND RESULTS: Thirty Japanese patients scheduled for elective coronary stent implantation were enrolled. Under low-dose ASA therapy, 300 mg clopidogrel was loaded on the 1(st) day and a daily 75-mg dose was administered on the following days. Assessed by optical aggregometer, rapid inhibition occurred at 4 h, when the inhibition of platelet aggregation rate (IPA) was 16.4+/-12.8% using 5 mumol/L ADP as the stimulus. The antiplatelet efficacy of clopidogrel was reasonably constant in each patient throughout the study period, although there was a broad inter-individual variation. At 48 h after clopidogrel loading, the ratios of responders (IPA > or =30%), hypo-responders (10%< or =IPA<30%), and non-responders (IPA <10%) were 36%, 50%, and 14%, respectively. CONCLUSIONS: The antiplatelet effectiveness of clopidogrel appeared individual-specific with wide inter-individual variation. The rate of clopidogrel non-responders was 14% among the examined Japanese patients.