Low-molecular-weight heparins: a decade with the new class of antithrombotic agents

Low molecular weight heparins (LMWH) are progressively replacing standard unfractionated heparin (UFH) for prophylaxis of venous thromboembolism, especially following surgery. LMWHs are also being used for treatment of established deep venous thrombosis. The main advantages of this new class of antithrombotic agents as compared with UFH are: 1) a new dosing concept (one single subcutaneous administration instead of two or three), based on improved bioavailability and prolonged half-life; 2) an improved efficacy: safety ratio both in the prophylactic and therapeutic settings. Despite these benefits, some unsolved issues remain to be addressed in specific clinical trials before LMWHs can definitively replace UFH in all previous indications of UFH. These issues include the use of LMWHs in patients with arterial thrombosis or myocardial infarction (e.g. in conjunction with thrombolytic treatment), and in patients with pulmonary embolism. In addition, the easy use of LMWHs opens the way towards outpatient therapy of proximal vein thrombosis but this modality needs to be fully assessed in well-designed clinical trials before definitive recommendations can be given.