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Aspirin's antiplatelet effect is caused by irreversible inhibition of platelet cyclooxygenase-1 (COX-1). In contrast, traditional nonsteroidal anti-inflammatory drugs (NSAIDs) bind reversibly to platelet COX and thus inhibit platelets only transiently. Researchers at the University of Pennsylvania examined whether appropriately timed NSAID therapy blocks aspirin's antiplatelet effect.
Healthy volunteers received aspirin (81 mg) at 8 am and ibuprofen (400 mg) at 10 am daily, for 6 days; after a 2-week washout period, the 2 drugs were given in reverse order. When aspirin preceded ibuprofen, COX-1 activity and platelet aggregation were inhibited nearly 100% throughout the ensuing 24 hours. However, when ibuprofen preceded aspirin, COX-1 activit…