Darexaban (YM150) is a direct inhibitor of coagulation factor Xa (FXa), discovered by Astellas Pharmaceuticals. FXa is a crucial serine protease in the coagulation cascade, responsible for the cleavage of prothrombin to its active form thrombin, which then converts soluble fibrinogen to insoluble fibrin, activates platelets and causes a formation of a blood clot. Darexaban inhibits factor Xa with a Ki value of 31 nM and shows anticoagulant activity in human plasma. In venous and A-V shunt thrombosis models in rats, darexaban strongly suppressed thrombus formation without affecting bleeding time. Darexaban was investigated in a number of clinical trials for prevention of venous thromboembolism in patients undergoing surgery, prevention of ischaemic events in acute coronary syndrome, prophylaxis of stroke in atrial fibrillation. In 2011 Astellas announced the discontinuation of darexaban because of high competition on anti-FXa drugs market.