Pharmacodynamic Assessment of Platelet Reactivity After a Loading Dose of Prasugrel or Clopidogrel in Patients With ST-Segment Elevation Myocardial Infarction

Background: Few studies have compared the platelet reactivity of prasugrel and clopidogrel in the acute phase of ST-segment elevation myocardial infarction (STEMI). Methods and Results: Primary percutaneous coronary intervention (PCI) was performed in 78 patients with STEMI within 12 h of onset. Patients were randomly assigned to receive a Japanese standard loading dose of prasugrel 20 mg or clopidogrel 300 mg. Platelet reactivity was serially assessed using the VerifyNow-P2Y12 assay, the results of which were expressed as P2Y12-reaction-units (PRU). PRU values were significantly lower in the prasugrel group (n=38) than in the clopidogrel group (n=40) at 3 h, 24 h, and 14 days after loading (191+/-101 vs. 271+/-50, 147+/-80 vs. 261+/-57, and 171+/-67 vs. 221+/-70, respectively, P<0.05), although the PRU levels at baseline (231+/-57 vs. 237+/-58, P=0.65) and 1 h after loading (282+/-65 vs. 291+/-62, P=0.54) were similar. As compared with the baseline values, the PRU levels at 1, 3 and 24 h after clopidogrel loading were significantly higher (respectively, P<0.05), whereas only the PRU at 1 h after prasugrel was elevated (P<0.001). Conclusions: In Japanese patients with STEMI who undergo primary PCI, prasugrel provides stronger platelet inhibition than clopidogrel from 3 h after loading, whereas platelet reactivity remained elevated within 24 h after clopidogrel loading.