Background Dual antiplatelet therapy with acetylsalicylic acid (ASA) and a P2Y12 ADP-receptor blocker is standard for prevention of coronary stent thrombosis. Clopidogrel, a 2nd-generation P2Y12 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 1st 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 μmol/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 ≥30%), hypo-responders (10%≤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. (Circ J 2009; 73: 336 - 342).
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