What is the recommended dosing of Enoxaparin (low molecular weight heparin) for an elderly patient with ST-Elevation Myocardial Infarction (STEMI) Acute Coronary Syndrome (ACS)?

Enoxaparin Dosing in Elderly STEMI Patients

For elderly patients ≥75 years with STEMI, administer enoxaparin 0.75 mg/kg subcutaneously every 12 hours WITHOUT an initial IV bolus, and further reduce to 1 mg/kg once daily if creatinine clearance is <30 mL/min. 1

Age-Specific Dosing Algorithm

For Patients ≥75 Years Old

• Omit the 30 mg IV bolus that is standard in younger patients 1, 2
• Administer 0.75 mg/kg subcutaneously every 12 hours (reduced from the standard 1 mg/kg dose) 1, 2
• The first subcutaneous dose should be given as soon as possible after presentation 1
• This dose reduction is critical because elderly patients have increased risk of intracranial hemorrhage with standard dosing 1, 3

For Patients <75 Years Old (For Comparison)

• Give 30 mg IV bolus initially 1, 4
• Follow with 1 mg/kg subcutaneously every 12 hours, with first SC dose within 15 minutes of the IV bolus 1, 4, 5

Renal Function Adjustments in Elderly Patients

If creatinine clearance <30 mL/min (regardless of age):

• Further reduce to 1 mg/kg subcutaneously once daily (every 24 hours instead of every 12 hours) 1, 2
• Consider using unfractionated heparin as an alternative in patients with known severe renal impairment 1

Clinical Context and Rationale

The dose reduction in elderly patients is based on the ExTRACT-TIMI 25 trial, which demonstrated that this modified regimen significantly reduced bleeding complications while maintaining efficacy 3. The trial showed:

• Bleeding risk amelioration: The relative risk of major bleeding with enoxaparin versus UFH was lower in patients ≥75 years (RR 1.15) compared to younger patients (RR 1.67) when using the reduced dose 3
• Maintained efficacy: Despite the dose reduction, enoxaparin remained superior to UFH for preventing death or recurrent MI in elderly patients, with an absolute benefit similar to younger patients 3
• Intracranial hemorrhage prevention: Earlier trials using standard dosing in elderly patients showed intracranial hemorrhage rates of 6.7% in patients 76-85 years old, which was reduced to 1.6% with the adjusted dosing regimen 1, 3, 6

Treatment Strategy Based on Reperfusion Approach

If Managed with Fibrinolysis:

• Use the age-adjusted dosing described above (0.75 mg/kg SC every 12 hours, no IV bolus) 1
• Continue for up to 8 days or until hospital discharge 5

If Undergoing Primary PCI:

• Enoxaparin 0.5 mg/kg IV bolus can be considered as an alternative to UFH in elderly patients 7
• Recent data from the ATOLL trial showed IV enoxaparin was safe in elderly patients undergoing primary PCI, with significantly lower minor bleeding rates compared to UFH 7

Critical Safety Considerations

Never switch between enoxaparin and UFH once treatment is initiated, as this increases bleeding risk substantially 1, 4

Monitor for bleeding complications more vigilantly in elderly patients, as they have:

• Higher baseline bleeding risk due to comorbidities 1
• Altered pharmacokinetics with lower anti-Xa exposure over time 3
• Increased risk of intracranial hemorrhage even with dose adjustments 1, 3

Assess renal function immediately in all elderly STEMI patients, as:

• Creatinine clearance <30 mL/min requires further dose reduction to once daily 1, 2
• Elderly patients frequently have unrecognized renal impairment 1
• Failure to adjust for renal function can lead to drug accumulation and bleeding 2

Common Pitfalls to Avoid

• Do not give the 30 mg IV bolus to patients ≥75 years—this is the most critical error and significantly increases bleeding risk 1, 2, 4
• Do not use the standard 1 mg/kg dose every 12 hours in elderly patients—always reduce to 0.75 mg/kg 1, 3
• Do not forget to assess creatinine clearance—elderly patients with renal impairment need once-daily dosing 1, 2
• Do not switch to UFH mid-treatment if bleeding concerns arise—this paradoxically increases bleeding risk 1, 4