Is enoxaparin (low molecular weight heparin) an appropriate anticoagulant for a patient with a history of myocardial infarction (heart attack)?

Enoxaparin for Myocardial Infarction

Enoxaparin is appropriate and superior to unfractionated heparin for patients with myocardial infarction, both in ST-elevation MI (STEMI) and non-ST-elevation MI (NSTEMI/unstable angina), with specific dosing adjustments required for elderly patients and those with renal impairment. 1

For STEMI Patients Receiving Fibrinolytic Therapy

Enoxaparin is the preferred anticoagulant over unfractionated heparin when fibrinolysis is the reperfusion strategy. 1

Efficacy Evidence

• The ExTRACT-TIMI 25 trial (n=20,506) demonstrated enoxaparin reduced death and reinfarction at 30 days compared to weight-adjusted UFH, with net clinical benefit favoring enoxaparin despite increased non-cerebral bleeding. 1
• The number needed to treat to prevent one death or MI at 30 days is 48. 2
• The net clinical benefit NNT is 20 (considering death, MI complication, or major bleeding), with 10% event rate for enoxaparin versus 15% for UFH. 2

Dosing Protocol for STEMI with Fibrinolysis

• Standard dose: 30 mg IV bolus followed by 1 mg/kg subcutaneously every 12 hours (maximum 100 mg for first two doses). 1, 3
• Elderly patients ≥75 years: NO IV bolus; reduce to 0.75 mg/kg subcutaneously every 12 hours (maximum 75 mg for first two doses). 1, 2, 3
• Renal impairment (CrCl <30 mL/min): 1 mg/kg subcutaneously every 24 hours. 1, 3
• Duration: Until revascularization if performed, or for at least 48 hours up to 8 days of hospitalization. 1

Critical Safety Consideration

The ASSENT-3 PLUS trial showed prehospital administration of standard-dose enoxaparin significantly increased intracranial hemorrhage in patients ≥75 years, making age-adjusted dosing mandatory. 1, 2

For STEMI Patients Undergoing Primary PCI

Enoxaparin may be preferred over unfractionated heparin for primary PCI based on the ATOLL trial. 1

Evidence for Primary PCI

• The ATOLL trial showed 17% reduction in the composite endpoint of 30-day death, MI complications, procedural failure, and major bleeding (P=0.063), with significant reductions in secondary endpoints including death, recurrent MI, or urgent revascularization. 1
• Importantly, no increase in bleeding was observed with enoxaparin versus UFH in the primary PCI setting. 1

Dosing for Primary PCI

• 0.5 mg/kg IV bolus followed by subcutaneous treatment. 1

For NSTEMI/Unstable Angina

Enoxaparin is superior to unfractionated heparin for unstable angina and non-Q-wave MI, reducing death and serious cardiac ischemic events. 1, 4, 5

Efficacy Evidence

• The TIMI 11B trial (n=3,910) showed enoxaparin reduced the primary endpoint (death, MI, or urgent revascularization) from 14.5% to 12.4% at 8 days (OR 0.83, P=0.048) and from 19.7% to 17.3% at 43 days (OR 0.85, P=0.048). 4
• Meta-analysis of TIMI 11B and ESSENCE trials demonstrated 20% reduction in death and serious cardiac ischemic events appearing within the first few days and sustained through 43 days. 5
• At 48 hours, there was 24% relative risk reduction (7.3% UFH vs 5.5% enoxaparin). 1

Dosing for NSTEMI/Unstable Angina

• Acute phase: 1.0 mg/kg subcutaneously every 12 hours (with or without initial 30 mg IV bolus depending on protocol). 4
• No increase in major hemorrhage during acute phase compared to UFH, though minor bleeding was higher. 4, 5

Bleeding Risk Profile

Major Bleeding Rates

• Major bleeding increases modestly with enoxaparin: 2.1% versus 1.4% with UFH. 2
• The number needed to harm for major bleeding is 143. 2
• During acute phase management (first 72 hours and initial hospitalization), no significant difference in major hemorrhage rates between enoxaparin and UFH. 4

Outpatient Phase Warning

Long-term outpatient enoxaparin treatment (beyond acute phase) showed increased major hemorrhage (2.9% vs 1.5% placebo, P=0.021) without additional relative benefit, and is therefore not recommended. 1, 4

Practical Advantages Over UFH

• No aPTT monitoring required, eliminating the complexity of maintaining therapeutic anticoagulation levels. 6, 7, 5
• Subcutaneous administration is simpler than continuous IV infusion. 6, 5
• More predictable pharmacokinetics with greater bioavailability and stable anticoagulation. 6, 7
• Lower incidence of heparin-induced thrombocytopenia compared to UFH. 7

Contraindication

Fondaparinux is not recommended for primary PCI (Class III recommendation). 1