The Synthetic Pentasaccharide Fondaparinux: First in the Class of Antithrombotic Agents that Selectively Inhibit Coagulation Factor Xa

Fondaparinux (Arixtra), a synthetic pentasaccharide, is the first in a new class of antithrombotic agents that selectively inhibit coagulation factor Xa. In vitro experiments demonstrated that it is a selective inhibitor of factor Xa. In plasma, fondaparinux selectively binds to antithrombin, catalyzes factor Xa inhibition, and thereby inhibits thrombin generation. Its antithrombotic efficacy has been demonstrated in various animal models mimicking venous and arterial thrombosis. In humans, its pharmacokinetic profile is favorable, with a rapid onset of antithrombotic activity and an elimination half-life allowing a convenient once-daily dosing regimen. In several clinical trials, fondaparinux was more effective than the reference drug, enoxaparin, in preventing venous thromboembolism after hip fracture, major knee, and elective hip replacement surgeries. The overall reduction in the risk of venous thromboembolism ranged between 26.3 and 56.4%, depending on the trial. This superior efficacy was achieved without increasing the risk of clinically relevant bleeding. Fondaparinux also showed promising results in the treatment of patients with venous thromboembolism and acute coronary syndromes. Thus, it is now established that selective factor Xa inhibition is an efficient way to prevent venous thrombosis. The advent of fondaparinux offers an opportunity to improve substantially the management of venous thromboembolism.