Thromboembolic prophylaxis is recommended to reduce the risk of stroke in patients with atrial fibrillation. Vitamin K antagonists (VKAs) such as warfarin are usually preferred, but aspirin is a commonly used alternative for patients unable or unwilling to take VKAs. The AVERROES trial compared apixaban, a factor Xa inhibitor, vs. aspirin for thromboembolic prophylaxis in 5,599 patients with atrial fibrillation unsuited to vitamin K antagonists. Patients were randomized to apixaban 5 mg twice daily vs. aspirin 81-324 mg/day. In the month prior to the trial, 76% had been taking aspirin and 15% had taken a VKA. At mean follow-up of 1.1 years, the overall risk of stroke was significantly reduced in the apixaban group (1.7% vs. 3.8%, p < 0.001, NNT 48) (level 1 [likely reliable] evidence). Apixaban was also associated with reduced rates of ischemic stroke (1.3% vs. 3.3%, p < 0.001, NNT 50), disabling or fatal stroke (1.1% vs. 2.6%, p < 0.001, NNT 67), and systemic embolism (0.007% vs. 0.5%, p = 0.01, NNT 203). There were no significant differences in all-cause mortality (4% vs. 5%, p = 0.07) or major bleeding (1.6% vs. 1.4%). The trial was stopped early at a preplanned interim analysis due to the reduced incidence of stroke in the apixaban group. Apixaban is not yet approved by the FDA (N Engl J Med 2011 Feb 10 early online).
For more information, see the Thromboembolic prophylaxis in atrial fibrillation topic in DynaMed.