What are the loading and maintenance doses for enoxaparin (low molecular weight heparin)?

Enoxaparin Loading and Maintenance Doses

For therapeutic anticoagulation, enoxaparin is administered at 1 mg/kg subcutaneously every 12 hours or 1.5 mg/kg subcutaneously once daily, with no separate loading dose required—the first subcutaneous injection serves as the initial dose. 1

Standard Therapeutic Dosing Regimens

Twice-Daily Regimen (Preferred for Most Indications)

• 1 mg/kg subcutaneously every 12 hours 1
• This is the most established regimen with the strongest evidence base 2
• Target anti-Xa level: 0.6-1.0 IU/mL (measured 4 hours post-dose) 3

Once-Daily Regimen (Alternative)

• 1.5 mg/kg subcutaneously once daily 1, 4
• Equivalent efficacy to twice-daily dosing for DVT/PE treatment 2
• Target anti-Xa level: 1.0-1.5 IU/mL (measured 4 hours post-dose) 3
• Offers improved compliance and reduced injection frequency 3

Special Context: ST-Elevation Myocardial Infarction (STEMI)

When enoxaparin is used with fibrinolytic therapy in STEMI, a specific loading dose protocol applies:

For Patients <75 Years Old

• Initial IV bolus: 30 mg 1
• Followed 15 minutes later by: 1 mg/kg subcutaneously every 12 hours (maximum 100 mg for first two doses) 1
• Continue for duration of hospitalization, up to 8 days 1

For Patients ≥75 Years Old

• No IV bolus 1
• 0.75 mg/kg subcutaneously every 12 hours (maximum 75 mg for first two doses) 1

Critical Dose Adjustments

Severe Renal Impairment (CrCl <30 mL/min)

• Therapeutic dosing: 1 mg/kg subcutaneously every 24 hours (not every 12 hours) 1, 4
• Prophylactic dosing: 30 mg subcutaneously once daily 1, 4, 5, 3
• Enoxaparin clearance is reduced by 44% in severe renal impairment 3

Obesity (BMI ≥40 kg/m²)

• 0.8 mg/kg subcutaneously every 12 hours 3
• Standard weight-based dosing may lead to excessive drug levels in morbidly obese patients 3

Prophylactic Dosing (For Context)

While the question asks about therapeutic dosing, prophylactic regimens differ substantially:

• Standard prophylaxis: 40 mg subcutaneously once daily 1, 4, 3
• High-risk patients or obesity: 40 mg subcutaneously every 12 hours 4, 3

Transition to PCI After Enoxaparin Therapy

If a patient on therapeutic enoxaparin requires percutaneous coronary intervention:

• If last dose was <8 hours ago: No additional enoxaparin needed 1
• If last dose was 8-12 hours ago: Give 0.3 mg/kg IV bolus 1
• If no prior enoxaparin: Give 0.5-0.75 mg/kg IV bolus 1

Monitoring Recommendations

Routine Monitoring

• Platelet count every 2-3 days from day 4 to day 14 to screen for heparin-induced thrombocytopenia 1, 3
• No routine aPTT monitoring required (unlike unfractionated heparin) 1

Anti-Xa Monitoring (When Indicated)

Anti-Xa monitoring is not routinely required but should be considered in specific populations 1, 3:

• Severe renal impairment on prolonged therapy 4, 3
• Pregnancy with therapeutic dosing 3
• Morbid obesity 3
• Measure 4 hours after injection, after 3-4 doses have been given 3

Duration of Therapy

• Minimum 5 days overlap with warfarin until INR ≥2.0 for at least 24 hours 1
• For STEMI: Continue for duration of hospitalization, up to 8 days 1
• For VTE: Typically 5-10 days initial treatment 3
• For cancer-associated VTE: Extended treatment for at least 3-6 months 3

Common Pitfalls to Avoid

Failure to adjust for renal function is the most critical error—always calculate creatinine clearance before initiating therapy, as standard dosing in severe renal impairment leads to drug accumulation and significantly increased bleeding risk 1, 4, 5, 3

Administering an unnecessary "loading dose"—enoxaparin does not require a separate loading dose for most indications; the first therapeutic subcutaneous injection provides immediate anticoagulation 2, 6

Switching between enoxaparin and unfractionated heparin—this increases bleeding risk and should be avoided 3

Timing with neuraxial anesthesia—enoxaparin must not be given within 10-12 hours before spinal/epidural procedures to prevent spinal hematoma 4, 3

Using fondaparinux dosing interchangeably—fondaparinux has completely different dosing (fixed 5/7.5/10 mg based on weight brackets) and should not be confused with enoxaparin's weight-based dosing 1