Inhibitory effects of ticagrelor compared with clopidogrel on platelet function in patients with acute coronary syndromes: the PLATO (PLATelet inhibition and patient Outcomes) PLATELET substudy.

OBJECTIVES: The PLATO (PLATelet inhibition and patient Outcomes) PLATELET substudy aimed to compare the antiplatelet effects of clopidogrel and ticagrelor in patients with acute coronary syndromes.

BACKGROUND: The PLATO study demonstrated superiority of ticagrelor over clopidogrel in the prevention of ischemic events in patients with acute coronary syndromes.

METHODS: Patients were randomized to receive either clopidogrel (300- to 600-mg loading dose [LD], 75 mg/day) or ticagrelor (180-mg LD, 90 mg twice daily). The effects of maintenance therapy were studied in 69 patients pre- and 2 to 4 h post-dose after at least 28 days. The LD effect was studied in 24 clopidogrel-naive patients. Light transmittance aggregometry (adenosine diphosphate 5 to 20 μM), VerifyNow P2Y12, and VASP phosphorylation assays were performed.

RESULTS: During maintenance therapy, ticagrelor achieved greater suppression of platelet reactivity compared with clopidogrel. The mean maximum light transmittance aggregometry responses (adenosine diphosphate 20 μM) post-maintenance dose were 44±15% for clopidogrel and 28±10% for ticagrelor (p<0.001). High platelet reactivity was seen more frequently in the clopidogrel group. Proton pump inhibitor use was associated with higher platelet reactivity with clopidogrel but not ticagrelor. The ticagrelor LD also achieved greater inhibition of platelet aggregation compared with the clopidogrel LD.

CONCLUSIONS: Ticagrelor achieves greater antiplatelet effect than clopidogrel in patients with acute coronary syndromes, both in the first hours of treatment and during maintenance therapy.