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Development of oral anticoagulants.

Warfarin has been the drug of choice for the prophylaxis and treatment of arterial and venous thrombotic disorders for over half a century [1]. It is the only oral anticoagulant currently approved for use in the US. Warfarin, a vitamin K antagonist, inhibits four vitamin K-dependent coagulation factors including prothrombin (factor II) and factors VII, IX and X through post-translational modification, and its anticoagulant effect is mainly due to down regulation of prothrombin and factor Xa [2]. Despite its well documented efficacy for the prevention of venous thromboembolism (VTE) after orthopaedic surgery and stroke prevention in patients with atrial fibrillation, warfarin has a narrow therapeutic window, with significant risks of haemorrhage at therapeutic concentrations. It has important limitations in clinical practice, including numerous drug and food interactions, slow onset of action, and more importantly the need for frequent laboratory monitoring to minimize the risk of inadequate anticoagulation and haemorrhagic events [3]. 
 
These limitations of warfarin have fostered a great interest in the development of novel anticoagulants for oral use to potentially replace warfarin. The design of specific inhibitors against molecular targets that play a pivotal role in the coagulation cascade has been the basis for a rational strategy for oral anticoagulant development [4]. The principal molecular targets are factor IIa (thrombin) and factor Xa. Two candidate compounds, one direct thrombin inhibitor (dabigatran etexilate developed by Boehringer Ingelheim) and one direct factor Xa inhibitor (rivaroxaban developed by Bayer), have entered phase III trials and are likely to emerge as new oral anticoagulants in the near future. A number of detailed review articles on the development of these oral anticoagulants has been recently published, shedding light on this fast growing field [5–7].