Comparison of idrabiotaparinux with vitamin K antagonists for prevention of thromboembolism in patients with atrial fibrillation: the Borealis-Atrial Fibrillation Study

Background Idrabiotaparinux, a long-acting inhibitor of factor Xa, was shown to be effective in the treatment of patients with venous thromboembolism. Objective To assess non-inferiority for the efficacy of idrabiotaparinux versus warfarin in patients with atrial fibrillation (AF) at risk of stroke and systemic embolism. Bleeding was also assessed. Methods This randomized, double-blind trial enrolled patients with electrocardiogram-documented AF. Idrabiotaparinux was administered weekly via subcutaneous injection, and warfarin was administered daily with dose adjustment to maintain the international normalized ratio between 2.0 and 3.0. Each idrabiotaparinux injection was 3mg for the first 7weeks, followed by 2mg thereafter, except in patients with a creatinine clearance of 30-50mLmin-1 or aged 75years. The patients received 1.5mg after the first 7weeks. The efficacy outcome was the composite of all fatal or non-fatal strokes and systemic embolism. The safety outcome was clinically relevant bleeding (major and clinically relevant non-major bleeding). Results The study was terminated prematurely by the sponsor for strategic/commercial, not scientific, reasons, with 39% of the planned number of patients included and an average duration of treatment of 240days. Of the 1886 idrabiotaparinux recipients, 20 developed stroke or systemic embolism (1.5% per year), whereas this occurred in 22 of the 1887 warfarin patients (1.6% per year, hazard ratio 0.98, 95% confidence interval 0.49-1.66). The annual incidence of bleeding was 6.1% in the idrabiotaparinux and 10.0% in the warfarin group (hazard ratio 0.61, 95% confidence interval 0.46-0.81). Conclusion If anything, despite its early termination, the idrabiotaparinux regimen studied suggested a comparable efficacy to dose-adjusted warfarin, with a lower bleeding risk.