Prevention of coagulation is required in a wide range of patients presenting with conditions such as venous thromboembolism, atrial fibrillation and acute coronary syndromes. Anticoagulants currently in clinical use include the parenterally administered unfractionated heparin and low molecular weight heparins (LMWHs) as well as the orally administered coumarins. Heparin and the LMWHs are indirect inhibitors of thrombin and factor Xa. The coumarins act by ...