What is the appropriate dosing of Enoxaparin (low molecular weight heparin) based on patient weight?

Enoxaparin Weight-Based Dosing

For therapeutic anticoagulation, administer enoxaparin at 1 mg/kg subcutaneously every 12 hours for standard-weight patients, with dose adjustments required for obesity, renal impairment, and prophylactic indications. 1, 2

Therapeutic Dosing (Treatment of VTE and ACS)

Standard Patients

• Administer 1 mg/kg subcutaneously every 12 hours for treatment of venous thromboembolism and acute coronary syndromes 1, 2
• For acute coronary syndrome specifically, consider a 30 mg intravenous bolus initially, followed by the standard 1 mg/kg subcutaneous dosing every 12 hours 1, 2
• This dosing has demonstrated equivalent or superior efficacy compared to unfractionated heparin 1, 3

Morbidly Obese Patients (Critical Adjustment)

Dose capping is necessary in obesity to avoid supratherapeutic levels and bleeding risk:

• BMI 40-50 kg/m²: Use approximately 0.97 mg/kg every 12 hours 4
• BMI 50-60 kg/m²: Reduce to 0.70 mg/kg every 12 hours 4
• BMI >60 kg/m²: Reduce to 0.71 mg/kg every 12 hours 4
• For patients weighing 100-139 kg, dosing at 0.75-0.85 mg/kg appears to be a safe starting range, though anti-Xa monitoring is essential due to high inter-patient variability 5
• Standard 1 mg/kg dosing in morbidly obese patients results in supratherapeutic levels in 53-65% of cases, necessitating dose reduction 4

Prophylactic Dosing (VTE Prevention)

Standard Patients

• Administer 40 mg subcutaneously once daily for general VTE prophylaxis 1, 2
• Alternative regimen: 30 mg subcutaneously twice daily 2

Morbidly Obese Patients (BMI ≥35 kg/m²)

• Use weight-based dosing at 0.5 mg/kg once daily rather than fixed-dose prophylaxis 2, 6
• This weight-based prophylactic regimen produces peak anti-Xa levels of approximately 0.25 units/mL (range 0.08-0.59), which is within or near the recommended prophylactic range without excessive anticoagulation 6
• Fixed-dose enoxaparin (40 mg daily) is likely inadequate in morbidly obese patients, as these patients were under-represented in clinical trials 6

Critical Dose Adjustments

Severe Renal Impairment (CrCl <30 mL/min)

• Reduce therapeutic dose to 1 mg/kg subcutaneously once daily (not twice daily) to avoid increased bleeding risk 1, 2
• This adjustment is essential as enoxaparin is renally cleared and accumulation occurs in renal dysfunction 1

Low Body Weight (<50 kg)

• Develop specific institutional dosing algorithms to avoid excessive anticoagulation 1
• These patients are at higher risk for supratherapeutic levels with standard weight-based dosing 1

Elderly Patients (≥75 years)

• Do not use enoxaparin in patients ≥75 years receiving fibrinolytic therapy due to significantly increased bleeding risk 1

Monitoring Recommendations

When to Monitor Anti-Xa Levels

• Routine anti-Xa monitoring is not required for standard dosing 1
• Monitor anti-Xa levels in: severe renal failure, pregnancy, obesity (especially BMI >40 kg/m²), and patients with extremes of body weight 1, 5, 4
• For obese patients on therapeutic dosing, monitoring is essential due to high inter-patient variability, with 53-65% achieving supratherapeutic levels at standard doses 4

Platelet Monitoring

• Monitor platelet counts during treatment to detect heparin-induced thrombocytopenia 1

Special Clinical Context: Cancer-Associated VTE

• Dalteparin is preferred over enoxaparin for cancer-associated VTE 1, 2
• If enoxaparin must be used, dose at 1 mg/kg every 12 hours, though long-term use at this dose has not been extensively tested in cancer patients 2

Critical Safety Considerations

• Never "stack" enoxaparin with unfractionated heparin due to markedly increased bleeding risk 2
• Major bleeding rates are similar across standard and weight-based dosing regimens (1.3-2.1%) when appropriately dosed 3
• In critically ill trauma patients, weight-based prophylactic dosing (0.6 mg/kg twice daily) achieves goal anti-Xa levels in 61% versus only 8% with standard dosing 7