Enoxaparin Dosing for Acute Myocardial Infarction
For initial therapy in acute MI, administer enoxaparin 1 mg/kg subcutaneously every 12 hours, with specific modifications based on age, renal function, and whether fibrinolytic therapy is used. 122
Standard Dosing Algorithm
For Initial Medical Management (No Fibrinolysis)
- Standard dose: 1 mg/kg subcutaneously every 12 hours
- Renal impairment (CrCl <30 mL/min): Reduce to 1 mg/kg subcutaneously once daily (every 24 hours)
- Continue until revascularization or for duration of hospitalization (up to 8 days) 122
For STEMI with Fibrinolytic Therapy
The dosing differs significantly based on age:
Patients <75 years old:
- 30 mg IV bolus initially
- Followed in 15 minutes by 1 mg/kg subcutaneously every 12 hours
- Maximum 100 mg for the first 2 subcutaneous doses 122
Patients ≥75 years old:
- No IV bolus (critical difference)
- 0.75 mg/kg subcutaneously every 12 hours
- Maximum 75 mg for the first 2 subcutaneous doses 122
Renal impairment (any age, CrCl <30 mL/min):
PCI-Specific Adjustments
If the patient proceeds to PCI, additional dosing depends on timing of last subcutaneous dose:
- Last dose 8-12 hours ago OR only 1 dose given: Administer 0.3 mg IV enoxaparin
- Last dose within 8 hours: No additional enoxaparin needed
- No prior enoxaparin: Give 0.5-0.75 mg/kg IV bolus 122
Evidence Quality and Rationale
The 2025 ACC/AHA/ACEP/NAEMSP/SCAI guidelines provide the most current and authoritative recommendations 122. These dosing regimens are based on landmark trials including ExTRACT-TIMI 25, which demonstrated that enoxaparin significantly reduced 30-day mortality and recurrent MI compared to unfractionated heparin in STEMI patients receiving fibrinolysis 3. The TIMI 11B and ESSENCE trials established efficacy in NSTE-ACS 45.
Critical Caveats
Age-related bleeding risk: The elimination of the IV bolus and dose reduction to 0.75 mg/kg in elderly patients (≥75 years) is essential to prevent major bleeding while maintaining efficacy 1223.
Renal dosing is mandatory: Failure to reduce dosing in severe renal impairment (CrCl <30 mL/min) significantly increases bleeding risk. Always calculate creatinine clearance before initiating therapy 122.
Weight-based dosing caps: The maximum doses for the first 2 subcutaneous injections (100 mg for age <75 mg for age ≥75) prevent excessive anticoagulation in heavier patients 122.
Timing matters for PCI: Administering additional enoxaparin at PCI when the last dose was <8 hours ago increases bleeding risk without added benefit 122.