Spotlight on Enoxaparin in ST-Segment Elevation Myocardial Infarction

Enoxaparin (enoxaparin sodium; Lovenox®) is a low-molecular-weight heparin (LMWH) that has recently been approved by the US FDA for use in patients with medically managed ST-segment myocardial infarction (STEMI), or STEMI with subsequent percutaneous coronary intervention. It binds to and potentiates the action of antithrombin, and inhibits coagulation factors XIa, IXa, Xa, and IIa (thrombin), thereby preventing formation of blood clots. Unfractionated heparin (UFH) has long been regarded as the antithrombotic agent of choice in the adjunctive treatment of patients with STEMI. However, compared with UFH, enoxaparin has many advantages in terms of its pharmacodynamic profile and, potentially, also its efficacy.

Enoxaparin was significantly more effective than UFH in patients presenting with STEMI who underwent fibrinolytic therapy in terms of the 30-day combined incidence of all-cause mortality plus recurrent nonfatal myocardial infarction (MI) [primary endpoint], and all-cause mortality plus recurrent nonfatal MI plus urgent revascularization (secondary endpoint) in the ExTRACT-TIMI 25 trial. The significant difference in the incidence of the composite primary endpoint between these two groups was maintained at the 1-year follow-up. Although bleeding was reported more frequently with enoxaparin than with UFH in the ExTRACT-TIMI 25 trial, enoxaparin was associated with a net clinical benefit relative to UFH. Patients in this trial received enoxaparin as an initial 30 mg intravenous bolus, followed by 1 mg/kg subcutaneously within 15 minutes and then every 12 hours for up to 8 days; the first two subcutaneous dosages were not to exceed 100 mg. Patients ≥75 years of age did not receive the initial bolus of enoxaparin and the 12-hourly dosages were reduced to 0.75 mg/kg; the dose was also reduced to 1 mg/kg every 24 hours in patients of any age who had an estimated creatinine clearance of <30 mL/min. Data from several earlier randomized, multicentre, phase III trials support these results.