Low-molecular-weight heparins

Low-molecular-weight heparins have proved to be both safe and effective for the prophylaxis and treatment of venous thromboembolism and show promise for prophylaxis and treatment of arterial thrombosis. Their pharmacokinetic advantages over unfractionated heparin have obviated the need for laboratory monitoring and have set the stage for the outpatient management of venous thrombosis. Although low-molecular-weight heparins have largely replaced unfractionated heparin in many parts of Europe, they are only beginning to find their niche in North America. Because they cause less heparin-induced thrombocytopenia and possibly less osteoporosis, the use of low-molecular- weight heparins is likely to increase over the coming years. There still is room for anticoagulants that are more potent. Like unfractionated heparin, low-molecular-weight heparins are unable to inactivate thrombin bound to fibrin, which may be an important trigger for clot extension at sites of vascular injury. This may explain why it has been difficult to show an advantage of low-molecular-weight heparins over unfractionated heparin in patients with unstable angina. The limitations of both low-molecular-weight heparins and unfractionated heparin have stimulated the development of new antithrombotic drugs, including hirudin, factor Xa inhibitors, tissue- factor-pathway inhibitor, and antagonists of glycoprotein IIb/IIIa, the platelet fibrinogen receptor. With these and newer drugs on the horizon, our ability to prevent and treat thrombotic diseases is likely to improve substantially.