The Effects of Aspirin and Acetaminophen on the Stomach in Healthy Volunteers

Low dose aspirin is used for the primary and secondary prevention of cardiovascular thromboembolic events. As a non-selective inhibitor of cyclooxygenase, aspirin use results in irreversible COX-1 inhibition leading to impaired platelet aggregation. However, aspirin also inhibits COX-1 activity in the gastric mucosa by suppressing the synthesis of protective prostaglandins. In doing so, this creates a state of propensity for the development of aspirin-associated gastrointestinal ulcers and ulcer complications. A high proportion of aspirin users also require concomitant use of anti-inflammatory medications for the treatment of pain and arthritis. However, evidence suggests that the risk of developing gastroduodenal ulcers and ulcer complications is significantly increased when aspirin is co-administered with other nonselective NSAIDs. In a previous study, concomitant aspirin (325 mg daily) in healthy subjects taking naproxen (500mg bid) was associated with endoscopic ulcer rates of 27.3% as compared to aspirin alone (7.6%). In a separate and independent trial of similar design, patients using 81 mg of aspirin in conjunction with daily naproxen also resulted in a higher incidence of gastric and duodenal ulcers than aspirin therapy alone. Beyond endoscopic ulcer rates, the risk of upper gastrointestinal hemorrhage has been reported to be substantially increased with concurrent administration of low-dose aspirin with nonselective NSAIDS. These data suggest that the gastrointestinal toxicity of combined aspirin with other NSAIDs may be more than additive.