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Eric S. Johnson, MPH; Stephan F. Lanes, PhD; Charles E. Wentworth III, MS; Margaret H. Satterfield, MSN; Bethlehem L. Abebe, BA; Linda W. Dicker, PhD

Arch Intern Med. 1999;159:1248-1253.

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 published randomized, placebo-controlled trials. We analyzed studies of patients who had recently had a transient ischemic attack or stroke (ie, secondary prevention). We abstracted data on the treatment regimen and stroke. To evaluate the dose-response relationship, we conducted a metaregression analysis of study-specific risk ratios by means of weighted linear regression.

Results  Eleven randomized, placebo-controlled trials contributed a total of 5228 patients randomized to aspirin only and 4401 patients randomized to placebo only. The slope of the dose-response curve was virtually flat across a wide range of aspirin doses from 50 to 1500 mg/d (P =.49 for test of slope0). Summarizing across studies, aspirin decreases the risk of 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 this 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.

From Epidemiology Resources Inc, Newton Lower Falls, Mass.

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