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Evidence summaries

Combined Aspirin-Oral Anticoagulant Therapy Compared with Oral Anticoagulant Therapy Alone Among Patients at Risk for Cardiovascular Disease

Except for patients with a mechanical heart valve, the benefits of oral anticoagulant (OAC) therapy plus aspirin in reducing thromboembolic events appear to be unclear compared with OAC alone, and there may be increased risk of major bleeding. Level of evidence: "B"

A systematic review 1 including 10 studies with a total of 4180 subjects was abstracted in DARE. The included studies contained patients with the following indications for treatment: mechanical heart valve, atrial fibrillation, coronary artery disease and high risk for cardiovascular disease. Low-dose aspirin (up to 100 mg/day) was used in 6 studies, and moderate to high doses (200 to 1000 mg/day) in 4 studies. The risk for arterial thromboembolism (myocardial infarction, unstable angina requiring hospitalisation, stroke, transient ischaemic attack or systemic embolism) was lower in patients receiving combined aspirin-OAC therapy compared with OAC therapy alone (OR 0.66, 95% CI 0.52 to 0.84; absolute risk reduction 2.5%, NNT 40). However, these benefits were limited to patients with a mechanical heart valve (OR 0.27, 95% CI 0.15 to 0.49). There was no difference in the risk for arterial thromboembolism with these treatments in patients with atrial fibrillation (OR 0.99, 95% CI 0.47 to 2.07) or coronary artery disease (OR 0.69, 95% CI 0.35 to 1.36). There was no difference in all-cause mortality with either treatment (OR 0.98, 95% CI 0.77 to 1.25).

The risk for major bleeding was higher in patients receiving aspirin-OAC therapy compared with OAC therapy alone (OR 1.43, 95% CI 1.00 to 2.02; absolute risk increase 1%, NNH 100). The subgroup analyses demonstrated a significantly greater incidence of major bleeding only in patients with a mechanical heart valve.

Comment: The quality of evidence is downgraded by imprecise results (limited study size for each comparison).

    References

    • Dentali F, Douketis JD, Lim W, Crowther M. Combined aspirin-oral anticoagulant therapy compared with oral anticoagulant therapy alone among patients at risk for cardiovascular disease: a meta-analysis of randomized trials. Arch Intern Med 2007 Jan 22;167(2):117-24. [PubMed] [DARE]

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