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Aspirin's antiplatelet effect occurs through irreversible inhibition of platelet cyclooxygenase-1 (COX-1). Because other nonsteroidal anti-inflammatory drugs (NSAIDs) inhibit COX-1 reversibly, they could block aspirin's antiplatelet effect if taken around the same time as aspirin. Investigators studied this interaction in nine healthy volunteers. Each volunteer received three 6-day courses of treatment: aspirin alone (100 mg daily at 8 am), 220 mg naproxen twice daily with 100 mg aspirin given 2 hours before the morning naproxen, and 220 mg naproxen twice daily with 100 mg aspirin given 2 hours after the morning naproxen. Each course was separated by a 2-week washout period.
Serum thromboxane B2 levels (which decrease following aspirin-induc…