The limitations of heparin and warfarin have prompted the development of new anticoagulant drugs for prevention and treatment of venous and arterial thromboembolism. Novel parenteral agents include synthetic analogs of the pentasaccharide sequence of heparin that mediates its interaction with antithrombin. Fondaparinux, the first synthetic pentasaccharide, is licensed for prevention of venous thromboembolism (VTE) after major orthopedic surgery and for initial treatment of patients with VTE. Idraparinux, a long-acting pentasaccharide that is administered subcutaneously once-weekly, is being compared with warfarin for treatment of VTE and for prevention of cardioembolic events in patients with atrial fibrillation. New oral anticoagulants include direct inhibitors of thrombin, factor Xa and factor IXa. Designed to provide more streamlined anticoagulation than warfarin, these agents can be given without routine coagulation monitoring. Ximelagatran, the first oral direct thrombin inhibitor, is as effective and safe as warfarin for prevention of cardioembolic events in patients with atrial fibrillation. However, ximelagatran produces a three-fold elevation in alanine transaminase levels in 7.9% of patients treated for more than a month, the long-term significance of which is uncertain. Whether other direct thrombin inhibitors or inhibitors of factors Xa or IXa also have this problem is under investigation. After a brief review of coagulation pathways, this paper focuses on new anticoagulants in advanced stages of clinical testing.
