Low molecular weight heparins in the treatment of unstable angina.

Unstable angina is in most cases caused by partial or complete coronary artery occlusion due to the disruption of an atherosclerotic plaque and resultant thrombus formation. Platelet aggregation and thrombin formation are key events in the development of acute coronary syndromes. An immediate antithrombotic approach is essential to prevent fatal and non-fatal myocardial infarction, and the combination of aspirin and unfractionated heparin has been the treatment of choice in the past years. Low molecular weight heparins have improved pharmacokinetic and pharmacodynamic properties over unfractionated heparin that have resulted in greater efficacy and safety in the field of venous thromboembolism. Low molecular weight heparins can be administered by subcutaneous injections at fixed, weight adjusted doses without need for monitoring. Three low molecular weight heparins have been tested in adequately sized clinical trials in patients with unstable angina and non-Q-wave myocardial infarction: nadroparin, dalteparin and enoxaparin. The results of the published trials have confirmed that the newer compounds are at least as safe and effective as unfractionated heparin offering considerable practical and clinical advantages. Low molecular weight heparins are currently recommended as alternative to unfractionated heparin in the acute management of acute coronary syndromes. Nevertheless, the different properties of these compounds and possibly the different designs of the clinical trials have resulted in apparent differences in clinical outcomes with the different agents. Direct comparisons are now required to determine the superiority of one compound over another.