Influence of Omeprazole and Famotidine on the Antiplatelet Effects of Clopidogrel in Addition to Aspirin in Patients With Acute Coronary Syndromes

BACKGROUND: It remains unclear whether concomitant use of omeprazole attenuates platelet function as compared with that of famotidine in patients with acute coronary syndromes (ACS) who receive clopidogrel. METHODS AND RESULTS: In this prospective study, 130 ACS patients treated with aspirin and clopidogrel who underwent stent implantation were randomly assigned to receive a Japanese standard dose of omeprazole 10mg daily or famotidine 20mg daily for at least 4 weeks. Between 14 and 28 days after enrollment, there was no significant difference in the platelet reactivity index (PRI) measured with vasodilator-stimulated phosphoprotein phosphorylation assay between the omeprazole group (n=65) and famotidine group (n=65) (55±17% vs. 51±19%; P=0.26). The cumulative rate of adverse cardiovascular events at 12 months was similar in the groups (13% vs. 17%; P=0.81). The PRI was similar (54.9±17.9% vs. 54.0±17.8%; P=0.83) in the omeprazole group (n=33) and the famotidine group (n=39) among patients with ST-elevation myocardial infarction (STEMI). However, there was a trend toward a higher PRI (55.2±15.9% vs. 46.4±19.4%; P=0.06) in the omeprazole group (n=32) as compared with the famotidine group (n=26) among patients without persistent ST-segment elevation ACS. CONCLUSIONS: As compared with famotidine, concomitant use of low-dose omeprazole does not significantly attenuate the antiplatelet effects of clopidogrel in patients with ACS, especially in those with STEMI.