Perspectives on antithrombotic agents: from unfractionated heparin to new antithrombotics.

Unfractionated heparin (UFH) has been the antithrombotic agent of choice for the prevention and treatment of venous thromboembolism (VTE) for a long time. UFH is also widely used for the treatment of patients with acute coronary syndromes. However, UFH has some limitations such as the need for parenteral administration and close monitoring of its anticoagulant effect. UFH is also associated with bleeding, heparin-induced thrombocytopenia and osteoporosis.Low molecular weight heparins (LMWHs) are produced by the depolymerization of UFH. LMWHs have pharmacologic advantages over UFH: a better bioavailability after subcutaneous administration, a longer plasma half-life and a more predictable anticoagulant effect. These improved features allow once or twice daily subcutaneous injection of weight-adjusted doses of LMWHs without requiring laboratory monitoring in patients with VTE or unstable angina.A number of new antithrombotic agents are currently under development. These include direct antithrombins and factor Xa inhibitors. The results of the main clinical trials with LMWHs as well as those of the studies with the new antithrombotic agents will be reviewed in this article.