Idraparinux is a synthetic analogue of the pentasaccharide moiety in heparin and low-molecular-weight heparin. Idraparinux specifically targets factor Xa. The half life is longer (80 hours) as it binds more tightly to antithrombin. Hence it is administered on a weekly basis. AMADEUS trial in studied 4576 patients with atrial fibrillation to check for the non-inferiority with warfarin (2.5 mg weekly vs vitamin K antagonists @ INR 2 – 3). The trial was stopped because of excess clinically relevant bleeding (21 cases of intracranial hemorrhages for Idraparinux vs 7 for vitamin K antagonists). But there was less thromboembolism (18 vs 27). [Amadeus Investigators, Bousser MG, Bouthier J, Büller HR, Cohen AT, Crijns H, Davidson BL, Halperin J, Hankey G, Levy S, Pengo V, Prandoni P, Prins MH, Tomkowski W, Thorp-Pedersen C, Wyse DG. Comparison of idraparinux with vitamin K antagonists for prevention of thromboembolism in patients with atrial fibrillation: a randomised, open-label, non-inferiority trial. Lancet. 2008.  26;371:315-21.]