Apixaban for the Prevention of Thromboembolic Events in Patients with Atrial Fibrillation: Primary Results of the ARISTOTLE Trial

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Background: Patients with atrial fibrillation are at risk for thromboembolism. Warfarin is effective but underused because of its narrow therapeutic window, risk of bleeding, and need for frequent monitoring. More effective, safer and easier to use anticoagulants are an unmet clinical need. Apixaban is an oral direct selective factor Xa inhibitor being investigated in patients with atrial fibrillation in the ARISTOTLE trial. Methods: Patients with atrial fibrillation and at least one additional risk factor for thromboembolism were randomized to blinded apixaban 5 mg BID or warfarin. Warfarin was adjusted to a target INR between 2 and 3 using a blinded encrypted bedside device. The primary efficacy endpoint was stroke (ischemic or hemorrhagic) or systemic embolism. The primary safety endpoint was ISTH major bleeding. A total of 448 patients with the primary endpoint were required for the primary non-inferiority analysis. The trial database was locked in March 2011. Results: A total of 18,201 patients were enrolled in 39 countries, including 336 from Japan. The mean time in therapeutic range (INR 2–3) with warfarin was 60–65%. A total of 447 patients had primary outcome events. ISTH major bleeding occurred in 789 patients. The primary results will be presented at the ESC in September 2011. Conclusions: The results of ARISTOTLE will define the role of apixaban in patients with atrial fibrillation.