Is the enoxaparin (low molecular weight heparin) dose for STEMI (ST-Elevation Myocardial Infarction) patients typically divided into intravenous and subcutaneous components?

Enoxaparin Dosing in STEMI: IV Bolus Plus Subcutaneous Administration

Yes, for STEMI patients under 75 years of age receiving fibrinolytic therapy, enoxaparin dosing is divided into an initial 30 mg intravenous bolus followed 15 minutes later by 1 mg/kg subcutaneous every 12 hours—not split equally as described in your example. 1

Correct Dosing Algorithm for STEMI

For Patients <75 Years Old:

• Initial dose: 30 mg IV bolus 1
• Followed by: 1 mg/kg subcutaneous every 12 hours, starting 15 minutes after the IV bolus 1
• Maximum: First two subcutaneous doses should not exceed 100 mg each 2, 3
• Duration: Continue for the duration of hospitalization, up to 8 days 1

For Patients ≥75 Years Old:

• No IV bolus is given 1
• Dose: 0.75 mg/kg subcutaneous every 12 hours 1
• Maximum: First two doses should not exceed 75 mg each 4

For Renal Impairment (Any Age):

• If creatinine clearance <30 mL/min: 1 mg/kg subcutaneous every 24 hours (not every 12 hours) 1
• Use Cockcroft-Gault formula to calculate creatinine clearance 1

Common Pitfall: The "Split Dose" Misconception

The example you described (splitting 0.6cc into 0.3cc IV and 0.3cc subcutaneous) is incorrect. 1 The IV bolus is a fixed 30 mg dose, not half of the total calculated dose. The subcutaneous dose is calculated separately based on body weight (1 mg/kg), and these are two distinct components of the regimen, not a split of the same dose.

Additional Dosing for PCI After Prior Enoxaparin

If a STEMI patient proceeds to PCI after receiving enoxaparin:

• If last dose was <8 hours ago: No additional enoxaparin needed 1, 4
• If last dose was 8-12 hours ago: Give 0.3 mg/kg IV bolus 1, 4
• If last dose was >12 hours ago: Treat as new anticoagulation 4

Evidence Quality

The ACC/AHA guidelines provide this dosing regimen with Level of Evidence A, based on the landmark ExTRACT-TIMI 25 trial which demonstrated superior efficacy of enoxaparin over unfractionated heparin in reducing death and recurrent MI at 30 days in STEMI patients receiving fibrinolytic therapy. 1, 2, 3 This regimen showed net clinical benefit despite slightly higher bleeding rates compared to UFH. 2, 3