Human gastric mucosal bleeding induced by low dose aspirin, but not warfarin.

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Abstract
OBJECTIVE--To investigate the suitability of treatment with low dose aspirin or warfarin, or both, as possible prophylaxis against cardiovascular disease by determining the effect on gastric mucosal bleeding. DESIGN--Randomised crossover trial. SETTING--Academic department of therapeutics. SUBJECTS--Twenty healthy male volunteers aged 19-22. INTERVENTIONS--On separate occasions and in randomised order all subjects received aspirin 75 mg, warfarin, or aspirin 75 mg combined with warfarin. Each treatment was given for 12 days or (when warfarin was used) for longer if necessary until the international normalised ratio of the prothrombin time was stable at 1.4-1.6. END POINT--Loss of blood over 10 minutes into gastric washings. MEASUREMENTS AND MAIN RESULTS--Bleeding over 10 minutes into gastric washings under baseline conditions and after five days, and at end of each regimen of treatment. Aspirin 75 mg increased bleeding from 0.60 (95% confidence interval 0.36 to 0.99) microliters/10 minutes to 1.26 (0.71 to 2.25) microliters/10 minutes at five days, with no evidence of either progressive change or adaptation thereafter. Warfarin had no effect on bleeding either alone or when combined with aspirin. CONCLUSIONS--Aspirin 75 mg causes gastric mucosal bleeding. Low dose warfarin neither induces gastric mucosal bleeding nor enhances that caused by aspirin.