Platelet inhibition after loading dose of prasugrel in patients with ST-elevation and non-ST-elevation acute coronary syndrome.

The PRASFIT-ACS study showed the antiplatelet effect 2-4 h after prasugrel loading. However, there is little information about the antiplatelet effect <2 h after prasugrel loading dose, especially in patients with acute coronary syndrome (ACS). There had not been any comparison between ST-segment elevation myocardial infarction (STEMI) and non-ST-segment elevation ACS (NSTE-ACS). Fifty patients with ACS (15 with STEMI and 35 with NSTE-ACS) were enrolled. They received a 20-mg prasugrel loading dose followed by a maintenance dose of 3.75 mg. Platelet reactivity [P2Y12 reaction units (PRU)] was evaluated by the VerifyNow assay at baseline, 30 min, 1, 2, 4, and 6 h, 1 week under prasugrel, and at 1 month after switching to clopidogrel. The primary end point was the change of PRU compared to the baseline. Furthermore, PRU after prasugrel loading between STEMI and NSTE-ACS was compared. A significant reduction in PRU from baseline was observed at ≥2 h after administration of prasugrel. In STEMI patients, a significant reduction in PRU was observed at 4 h after prasugrel loading. STEMI patients had higher PRU compared to NSTE-ACS patients at 2, 4, and 6 h after prasugrel loading. Utilizing >208 PRU as a cutoff value, STEMI patients had a higher prevalence of high on-treatment platelet reactivity at 2-6 h and 1 week after loading. Rapid antiplatelet effect is not achieved by low-dose prasugrel loading in STEMI patients. Platelet inhibition occurs earlier in NSTE-ACS patients, although it takes ≥2 h after loading in the majority of patients.