Bleeding risk in randomized controlled trials comparing warfarin and aspirin: a systematic review and meta-analysis

Warfarin and aspirin (acetylsalicylic acid [ASA]) are the most commonly used anticoagulant and antiplatelet drugs in the treatment of cardiovascular disease.

To provide a pooled estimate of the bleeding risk from randomized controlled trials (RCTs) comparing warfarin and ASA at the dose ranges recommended in evidence-based guidelines.

Ovid MEDLINE, Embase and the Cochrane Library, up to September 2011, were searched for RCTs comparing bleeding rates in adult patients randomized to warfarin, target International Normalized Ratio (INR) 2.0-3.5, and ASA, 50-650 mg daily, with at least 3 months of follow-up. Pooled odds ratios (ORs) and associated 95% confidence intervals (CIs) were calculated with the inverse variance method and the random effects model.

Four thousand four hundred and forty-two abstracts were screened, resulting in eight included studies for final analysis. A pooled estimate derived from the 2904 patients enrolled indicated a trend towards an increase in major bleeding risk in those randomized to warfarin (OR 1.27; 95% CI 0.83-1.94). The pooled OR for intracranial hemorrhage in patients treated with warfarin vs. ASA was 1.64 (95% CI 0.71-3.78), and that for extracranial major bleeding was 1.03 (95% CI 0.61-1.75). Minor bleeding, from a 1748-patient sample, was more common in warfarin patients (OR 1.50; 95% CI 1.13-2.00).

This meta-analysis failed to find a statistically significant difference in major bleeding between warfarin, target INR 2.0-3.5, and ASA, 50-650 mg daily. The trend towards increased bleeding with warfarin appears to be explained by an excess of intracranial bleeding in warfarin patients.