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

Abstract

The PRASFIT-ACS study showed the antiplatelet effect 2-4h after prasugrel loading. However, there is little information about the antiplatelet effect <2h 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 3.75mg. Platelet reactivity [P2Y12 reaction units (PRU)] was evaluated by the VerifyNow assay at baseline, 30min, 1, 2, 4, and 6h, 1week under prasugrel, and at 1month 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 ≥2h after administration of prasugrel. In STEMI patients, a significant reduction in PRU was observed at 4h after prasugrel loading. STEMI patients had higher PRU compared to NSTE-ACS patients at 2, 4, and 6h after prasugrel loading. Utilizing >208 PRU as a cutoff value, STEMI patients had a higher prevalence of high on-treatment platelet reactivity at 2-6h and 1week 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 ≥2h after loading in the majority of patients.