A metaregression analysis of the dose-response effect of aspirin on stroke

Background: We evaluated whether the risk of stroke depends on aspirin dose in patients with a previous transient ischemic attack or stroke. Methods: We conducted a metaregression analysis of stroke by using publishe d randomized, placebo-controlled trials. We analyzed studies of patients wh o had recently had a transient ischemic attack or stroke (ie, secondary pre vention). We abstracted data on the treatment regimen and stroke. To evalua te the dose-response relationship, we conducted a metaregression analysis o f study-specific risk ratios by means of weighted linear regression. Results: Eleven randomized, placebo-controlled trials contributed a total o f 5228 patients randomized to aspirin only and 4401 patients randomized to placebo only. The slope of the dose-response curve was virtually flat acros s a nide range of aspirin doses from 50 to 1500 mg/d (P = .49 for test of s lope not equal 0). Summarizing across studies, aspirin decreases the risk o f stroke by about 15% (risk ratio, 0.85; 95% confidence interval, 0.77-0.94 ). Conclusions: Aspirin reduces the risk of stroke by approximately 15%, and t his effect is uniform across aspirin doses from 50 to 1500 mg/d. The lowest effective aspirin dose has not yet been identified, but it could be lower than 50 mg/d.