What is the clinical evidence from this study?

Study design: Meta-Analysis. Population: Previous transient ischemic attack or stroke (n=9629). Intervention: Aspirin vs. Placebo. Primary outcome: Stroke (RR 0.85, 95% CI 0.77-0.94).

June 14, 1999

A Metaregression Analysis of the Dose-Response Effect of Aspirin on Stroke

Key Result

Aspirin reduces the risk of stroke by 15% (RR 0.85; 95% CI 0.77-0.94) in patients with previous TIA or stroke, with a uniform effect across doses from 50 to 1500 mg/d (P=0.49 for slope).

Study Design

Type

Meta-Analysis (n=9,629)

Structured PICO

Does the risk of stroke depend on aspirin dose in patients with a previous transient ischemic attack or stroke?

Population

9,629 patients (from 11 randomized, placebo-controlled trials) with a previous transient ischemic attack or stroke (secondary prevention)

Intervention

Aspirin only, doses ranging from 50 to 1500 mg/d

Comparator

Placebo only

Outcome

Strokehard clinical

Aspirin reduces the risk of stroke by approximately 15% in secondary prevention, with no significant difference in efficacy across doses ranging from 50 to 1500 mg/d.

Main Result

Effect estimate: RR 0.85 (95% CI 0.77-0.94)

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.

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