A critical review of clinical trials for low-molecular-weight heparin therapy in unstable coronary artery disease.

Unstable angina and non-ST-segment elevation myocardial infarction (MI) are collectively referred to as unstable coronary artery disease (UCAD). They are conditions that share a common pathophysiology and represent frequently encountered, potentially life-threatening clinical manifestations of advanced atherosclerosis. Therefore, treatment of UCAD is a major focus for practicing clinicians, and although pharmacologic agents have been developed that impact on patient outcome, recent data suggest that a further reduction in ischemic complications is possible. Acute-phase treatment with aspirin is associated with a significant reduction in death and nonfatal MI in patients with UCAD. This benefit is enhanced by the addition of unfractionated heparin (UFH) to the treatment strategy; however, UFH requires careful monitoring and titration. In contrast, low-molecular-weight heparins (LMWHs), produced by chemical or enzymatic depolymerization of UFH, yield a predictable and consistent pharmacokinetic profile and anticoagulant response, making them an attractive treatment alternative to UFH in patients with UCAD. The optimal duration of treatment with LMWH is an important question influenced by the observation that reactivation of coagulation occurs following the early and abrupt discontinuation of heparin treatment. Early trials, such as FRISC and FRIC, demonstrated the benefit of acute therapy with dalteparin sodium; however, the results of extended treatment with dalteparin were inconclusive. The extended phase of these studies included relatively low-risk patients, and a once-daily, relatively low-dose strategy was employed. The findings derived from the FRISC II trial, which used a twice-daily dose of dalteparin, suggest a benefit for at least 60 days with extended treatment in high-risk patients with UCAD. Although an early-invasive treatment strategy is particularly beneficial, patients in whom early revascularization is not possible should be considered for extended treatment with dalteparin for up to 45 days, especially those awaiting percutaneous coronary intervention. Extended treatment with dalteparin therefore provides a protective "bridge" to enhance the outcome of patients with UCAD awaiting revascularization.