Heterogeneity of Synthetic Factor Xa Inhibitors

Heparins and vitamin K antagonists are the landmarks of antithrombotic treatment. Both of them were discovered by serendipity; they are multi-targeted drugs and share several limitations. New molecules have been designed in order to be both more selective concerning their biological target and more homogeneous in their biochemical structure aiming at an improved benefit/risk ratio in the treatment of thrombotic disease. In this article, we will review the pharmacological characteristics of the new synthetic direct or antithrombin dependent inhibitors of FXa in the light of the modern concept of blood coagulation process. We will also present the most recent data from the clinical trials with synthetic inhibitors of FXa. Among them, the synthetic pentasaccharide fondaparinux is the first synthetic and specific FXa inhibitor, which has been approved by health authorities in Europe and in the USA for the prophylaxis of venous thromboembolism in major orthopaedic surgery and is being approved for the treatment of pulmonary embolism and DVT as a single daily subcutaneous injection. The phase II dose-finding trial of the "metapentasaccharide" idraparinux administered subcutaneously once weekly in the secondary prevention of VTE has been completed. DX-9065a is the first direct synthetic inhibitor which has been studied in patients with coronary disease. Razaxaban, BAY59-7939, ZK-807834 and JTV-803 are orally active direct FXa inhibitors, which have been studied in phase II trials. Several other synthetic direct inhibitors of FXa (such as FXV673, YM60828, KFA-1411) are in a preclinical stage of research. From a clinical point of view, the results of recent trials with the synthetic specific FXa inhibitors clearly show that the inhibition of FXa is a critical point in the antithrombotic strategy.