Background: High on-treatment platelet reactivity in patients with acute coronary syndromes is associated with adverse outcomes. The purpose of this study was to compare the anti-platelet effect of prasugrel and 3 different dosing regimens of clopidogrel in "real world" STEMI patients undergoing primary PCI.
Methods: Platelet reactivity was assessed with light transmitted aggregometry on the third day post clopidogrel loading in 372 consecutive STEMI patients eligible for prasugrel therapy: 119 pts were treated with standard regimen (300 mg loading, 75 mg/day maintenance dose); 56 with a high loading dose alone (600 mg loading, 75 mg/day maintenance dose); 74 with a high loading/high maintenance dose (600 mg loading, 150 mg/day maintenance); and 123 pts were treated with prasugrel (60 mg loading, 10 mg/day maintenance).
Results: More aggressive clopidogrel dosing regimens resulted in resulted in significantly lower mean platelet reactivity to ADP (59±18; 45±16; and 39±16 for 300/75; 600/75 and 600/150 respectively, p<0.02 for all comparisons), and lower proportion of patients exhibiting clopidogrel hypo-responsiveness (32%; 7%; and 7% for 300/75; 600/75 and 600/150 respectively, p<0.001 for comparison with 300/75). However, as compared with the most aggressive clopidogrel dosing regimen (600 mg loading and 150 mg/day maintenance), standard dose prasugrel resulted in significantly lower platelet reactivity to ADP (39±16 vs 31±17, p=0.04), and lower proportion of patients exhibiting clopidogrel hypo-responsiveness (7% vs 3.3%, p=0.03).
Conclusion: In STEMI patients, increasing clopidogrel dose results in greater platelet inhibition. However, prasugrel results in significantly greater platelet inhibition than that achieved by all clopidogrel dosing regimens.
