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 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.
Johnson
E S
ES
Epidemiology Resources Inc, Newton Lower Falls, Mass 02162, USA. epidemiol@aol.com
Lanes
S F
SF
Wentworth
C E
CE
Satterfield
M H
MH
Abebe
B L
BL
Dicker
L W
LW
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
D005343:Fibrinolytic Agents; D010975:Platelet Aggregation Inhibitors; D001241:Aspirin