Enoxaparin Dosing in STEMI
For STEMI with Fibrinolytic Therapy
For patients under 75 years receiving fibrinolytic therapy, administer a 30 mg IV bolus of enoxaparin followed 15 minutes later by 1 mg/kg subcutaneously every 12 hours (maximum 100 mg for first two doses). 1, 2
Age-Based Dosing Algorithm
Patients <75 years:
- 30 mg IV bolus initially 1, 2
- Wait 15 minutes, then give 1 mg/kg subcutaneously every 12 hours 1, 2
- Maximum 100 mg for the first two subcutaneous doses only 1, 2
Patients ≥75 years:
- No IV bolus (this is critical—omit the bolus entirely) 1, 2
- 0.75 mg/kg subcutaneously every 12 hours 1, 2
- Maximum 75 mg for the first two doses 1, 2
This age-based modification stems from increased intracranial hemorrhage risk in elderly patients documented in randomized trials. 1
Renal Dosing Adjustments
For creatinine clearance <30 mL/min (regardless of age):
- 1 mg/kg subcutaneously once daily (not every 12 hours) 1, 2
- Calculate creatinine clearance in all patients before initiating therapy 3
Duration of Therapy
- Continue for the index hospitalization, up to 8 days or until revascularization 1, 2
- Minimum duration is 48 hours 1
For STEMI with Primary PCI (No Fibrinolysis)
Enoxaparin may be considered as a safe alternative to unfractionated heparin for patients undergoing primary PCI. 1
Timing-Based Dosing at PCI
The timing of the last enoxaparin dose relative to PCI determines additional dosing needs:
If last subcutaneous dose was <8 hours before balloon inflation:
- No additional enoxaparin needed 2
If last subcutaneous dose was 8-12 hours before balloon inflation:
- Give 0.3 mg/kg IV bolus at time of PCI 3
If last subcutaneous dose was >12 hours before balloon inflation:
- Give 0.3 mg/kg IV bolus at time of PCI 2
Research data from the FINESSE trial substudy demonstrated that enoxaparin (0.5 mg/kg IV, 0.3 mg/kg SC) was associated with lower major bleeding (2.6% vs 4.4%) and reduced death/MI/urgent revascularization (5.3% vs 8.0%) compared to UFH in primary PCI. 4 The MITRA-plus registry similarly showed reduced mortality (1.6% vs 6.0%) and reinfarction (1.9% vs 3.8%) with enoxaparin versus UFH in primary PCI. 5
Critical Safety Considerations
Anticoagulant Switching is Contraindicated
Never switch between enoxaparin and UFH in either direction—this significantly increases bleeding risk. 1
Once enoxaparin is started, continue it throughout hospitalization. 1 The ACC/AHA guidelines give this a Class III recommendation (meaning it causes harm). 1
Common Pitfalls to Avoid
- Giving IV bolus to patients ≥75 years: The bolus is omitted entirely in elderly patients due to intracranial hemorrhage risk 1, 2
- Failing to reduce dose in renal impairment: Patients with CrCl <30 mL/min require once-daily dosing instead of twice-daily 1, 2
- Adding UFH during PCI in patients already on enoxaparin: This "stacking" dramatically increases bleeding complications 3
- Using every-12-hour dosing in severe renal impairment: Must switch to once-daily dosing 1, 2
Evidence Quality
The 2013 ACC/AHA STEMI guidelines provide Class I, Level of Evidence A recommendations for enoxaparin use with fibrinolytic therapy. 1 Nine randomized trials and meta-analyses document similar or improved composite outcomes (death, MI, recurrent ischemia) when enoxaparin was used instead of UFH in STEMI patients receiving fibrinolysis. 1 The ENTIRE-TIMI 23 trial demonstrated that enoxaparin achieved similar TIMI 3 flow rates as UFH while reducing death/recurrent MI from 15.9% to 4.4% (p=0.005) with full-dose tenecteplase. 6