The use of anticoagulation therapy for obese patients with atrial fibrillation (AF) who are at increased risk for stroke is challenging. Recent guidelines caution against the use of non-vitamin K antagonists oral anticoagulants (NOACs) in patients with extreme body weight (≥120kg) due to lack of data in this group. Our aim is to study the efficacy and safety of apixaban versus warfarin in obese patients with AF.

The Apixaban for Reduction in Stroke and Other Thromboembolic Events in Atrial Fibrillation (ARISTOTLE) study was a randomized trial, comparing apixaban with warfarin in 18,201 patients with atrial fibrillation and at least one additional risk factor for stroke. The primary efficacy and safety outcomes were stroke or systemic embolism and ISTH major bleeding. Death from any cause was a secondary endpoint. We estimated the randomized treatment effect (apixaban vs. warfarin) stratified by body weight (<120kg, ≥120kg) using a Cox regression model.

Of the 18,139 patients who had weight and outcomes data recorded, 17,104 (94%) patients were<120kg and 1035 (6%) had a weight≥120kg. Fifty percent of patients≥120kg were randomized to apixaban. Patients in the extreme body weight group were younger (median 62 years, IQR 56–97 vs 70 years, IQR 63–76; P<0.001), less commonly female (15.8% vs 36.4%; P<0.001), with a lower CHADS2 (mean 1.95, SD 0.93 vs 2.13, SD 1.11) than patients<120kg.

The efficacy and safety of apixaban versus warfarin appear to be similar in patients with extreme body weight when compared with non-obese subgroup of patients. Larger studies of patients with extreme body weight treated with NOACs are warranted.