Enoxaparin Dosing in STEMI
Standard Dosing for STEMI with Fibrinolytic Therapy
For patients under 75 years receiving fibrinolytic therapy for STEMI, administer a 30 mg IV bolus of enoxaparin followed 15 minutes later by 1 mg/kg subcutaneously every 12 hours, with a maximum of 100 mg for the first two doses. 1
Age-Based Modifications
- Patients ≥75 years should NOT receive the IV bolus and instead receive 0.75 mg/kg subcutaneously every 12 hours, with a maximum of 75 mg for the first two doses. 1, 2, 3
- This age-based modification is critical because elderly patients have significantly increased risk of intracranial hemorrhage, as documented in nine randomized trials and meta-analyses. 1
Renal Dosing Adjustments
- For creatinine clearance <30 mL/min, reduce to 1 mg/kg subcutaneously once daily (instead of twice daily) regardless of age. 1, 2, 3
- Calculate creatinine clearance in all STEMI patients before initiating enoxaparin, as renal impairment dramatically affects drug clearance. 4
- Enoxaparin clearance decreases by 31% in moderate renal impairment and 44% in severe renal impairment, leading to significant drug accumulation with standard dosing. 4
Duration of Therapy
- Continue enoxaparin throughout hospitalization or for up to 8 days. 1, 2, 3
- Never switch between enoxaparin and unfractionated heparin in either direction - this carries a Class III recommendation (causes harm) due to significantly increased bleeding risk. 1
STEMI with Primary PCI (No Fibrinolysis)
- Enoxaparin may be used as an alternative to unfractionated heparin for patients undergoing primary PCI, though this is less well-established than its use with fibrinolytic therapy. 1
Critical Safety Considerations
Bleeding Risk Management
- The ExTRACT-TIMI 25 trial demonstrated that enoxaparin reduces death and recurrent MI compared to UFH, despite slightly higher bleeding rates, resulting in net clinical benefit. 2, 3, 5
- Major bleeding occurs in approximately 1.9-2.4% of patients with full-dose fibrinolytic therapy. 5
- Do not administer UFH to patients already on enoxaparin - this "stacking" significantly increases bleeding complications. 6
Common Pitfalls to Avoid
- Failure to adjust for age ≥75 years - omitting the IV bolus and reducing the subcutaneous dose is mandatory to prevent intracranial hemorrhage. 1, 2, 3
- Failure to adjust for renal impairment - patients with CrCl <30 mL/min require once-daily dosing to prevent drug accumulation and bleeding. 1, 4
- Switching anticoagulants - transitioning between enoxaparin and UFH dramatically increases bleeding risk and should be avoided. 1
- Exceeding maximum doses - the first two subcutaneous doses should not exceed 100 mg in patients <75 years or 75 mg in patients ≥75 years. 2, 3