Influence of omeprazole and famotidine on the antiplatelet effects of clopidogrel in addition to aspirin in patients with acute coronary syndromes: a prospective, randomized, multicenter study.

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. 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. 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.