Fondaparinux: a synthetic heparin pentasaccharide as a new antithrombotic agent

Abstract

Fondaparinux (Arixtra®, Sanofi-Synthélabo/Organon) is the first of a new class of antithrombotic agents distinct from low molecular weight heparins (LMWHs) and heparin. It is a chemically synthetic pentasaccharide mimicking the site of heparin that binds to antithrombin III (AT). It exhibits only factor (F) Xa (FXa) inhibitor activity via binding to AT, which in turn inhibits thrombin generation. In contrast to heparin and LMWH, plasma anti-Xa activity corresponds directly to levels of fondaparinux. It does not release tissue factor pathway inhibitor (TFPI). There is nearly complete bioavailability by the sc. route, rapid onset of action, a prolonged half-life in both iv. and sc. (14 - 20 h) dosing regimens and no metabolism preceding renal excretion. Phase IIb clinical studies have identified a dose of 2.5 mg once-daily for prophylaxis of venous thrombosis. Four Phase III studies (n > 7000) have demonstrated a combined 50% relative risk reduction of venous thromboembolic events in orthopaedic surgery pat...