Fondaparinux, the first selective factor Xa inhibitor.

Fondaparinux (Arixtra, Sanofi-Synthelabo, Paris, France) is a pentasaccharide that selectively inhibits factor Xa; it is the first of a new class of synthetic antithrombotic agents. Fondaparinux has a linear pharmacokinetic profile allowing once-daily subcutaneous administration. Absence of metabolism, complete bioavailability, and lack of nonspecific binding in plasma contribute to the predictability of its effect. Fondaparinux has been approved for use in the prophylaxis of venous thromboembolism following orthopedic surgery. In this setting, it was found to reduce VTE risk by more than 50% in comparison with the low molecular weight heparin enoxaparin, with an incidence of clinically important bleeding not significantly different from that of standard low molecular weight heparin regimens. Furthermore, 4 weeks of prophylaxis with fondaparinux after hip fracture surgery was shown to reduce the risk of venous thromboembolism by 96% compared with 1-week prophylaxis. Finally, the efficacy and safety of fondaparinux in the treatment of venous thromboembolism and acute coronary syndromes appears promising.