Omeprazole does not interfere with the antiplatelet effect of low-dose aspirin in man

Background: Experimental studies have shown that omeprazole and other anti-inflammatory agents compromise the therapeutic activity of nonsteroidal anti-inflammatory drugs and aspirin in rats. It is not known whether this effect will occur in humans. Our aim was to determine whether omeprazole affects the antiplatelet effects of low-dose aspirin in humans. Methods: Platelet lumiaggregation, skin bleeding time, plasma levels of aspirin and salicylic acid, and serum gastrin levels were determined in 14 healthy men before and after the ingestion of 125 mg aspirin with or without previous treatment with 20 mg/day of omeprazole for 4 days before testing. Results: Omeprazole increased serum gastrin levels from 64 (median: range, 52-91) pg/ml to 80.5 (median: range, 56-455) pg/ml (P < 0.05) but did not significantly affect the plasma concentration of aspirin or salicylic acid. Aspirin increased skin bleeding time in all subjects, and the increase was similar with and without previous omeprazole treatment. Aspirin inhibited platelet aggregation in response to both collagen and arachidonic acid regardless of omeprazole treatment. Conclusion: A single dose of 20 mg omeprazole daily does not interfere with the biologic activity of 125 mg aspirin on platelets in humans.