title: A metaregression analysis of the dose-response effect of aspirin on stroke.
abstract: 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 slope not =0). 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.
authors.affiliation: Epidemiology Resources Inc, Newton Lower Falls, Mass 02162, USA. epidemiol@aol.com
authors.forename: E S
authors.initials: ES
authors.lastname: Johnson
authors.forename: S F
authors.initials: SF
authors.lastname: Lanes
authors.forename: C E
authors.initials: CE
authors.lastname: Wentworth
authors.forename: M H
authors.initials: MH
authors.lastname: Satterfield
authors.forename: B L
authors.initials: BL
authors.lastname: Abebe
authors.forename: L W
authors.initials: LW
authors.lastname: Dicker
mesh_terms: D000368:Aged; D001241:Aspirin / Q000008:administration & dosage*; D002561:Cerebrovascular Disorders / Q000517:prevention & control*; D004305:Dose-Response Relationship, Drug; D005260:Female; D005343:Fibrinolytic Agents / Q000008:administration & dosage*; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D010975:Platelet Aggregation Inhibitors / Q000008:administration & dosage*; D016032:Randomized Controlled Trials as Topic; D012306:Risk
chemical_list: D005343:Fibrinolytic Agents; D010975:Platelet Aggregation Inhibitors; D001241:Aspirin