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.