Background and Aims: The safety of low-dose daily aspirin therapy in the gastrointestinal tract is uncertain. Our objectives were to evaluate the long-term effects of very low daily aspirin doses in the gastrointestinal tract and effects on platelet-derived serum thromboxane levels in volunteers. Methods: Subjects were randomized to receive 10 mg (n = 8), 81 mg (n = 11), or 325 mg (n = 10) aspirin daily for 3 months. Before administration of aspirin, all subjects underwent gastroduodenoscopy, and most underwent proctoscopy for assessment of mucosal injury and prostaglandin content. After 1.5 and 3 months, subjects again underwent gastroduodenoscopy and, at 3 months, another proctoscopy. Results: Each aspirin dose (even 10 mg) significantly reduced gastric mucosal prostaglandin levels, to ~40% of the baseline value. All three doses also induced significant gastric injury, and 325 mg caused duodenal injury. Three subjects developed gastric ulcers, 1 while taking 10 mg/day of aspirin. Furthermore, aspirin at 81 mg/day and 325 mg/day (but not 10 mg/day) significantly reduced duodenal mucosal prostaglandin levels to ~40% of the baseline value. Only 325 mg of aspirin per day significantly reduced rectal mucosal prostaglandin levels to ~60% of the baseline value. Serum thromboxane levels were inhibited 62%, 90%, and 98% with 10, 81, and 325 mg of aspirin. Conclusions: The findings explain aspirin's predominant gastric toxicity and question the safety of even 10 mg of aspirin daily.
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