How is the dose of Lovenox (enoxaparin) calculated?

Enoxaparin (Lovenox) Dosing Calculation

Enoxaparin dosing is calculated based on body weight at 1 mg/kg subcutaneously every 12 hours for treatment of acute coronary syndromes and venous thromboembolism, with specific adjustments required for age ≥75 years (0.75 mg/kg every 12 hours) and severe renal impairment (1 mg/kg every 24 hours for creatinine clearance <30 mL/min). 1, 2

Standard Treatment Dosing Algorithm

Step 1: Determine Clinical Indication

For acute coronary syndromes (NSTEMI/unstable angina):

• Initial IV bolus: 30 mg 1
• Followed immediately by: 1 mg/kg subcutaneously every 12 hours 1
• Maximum dose for first two subcutaneous injections: 100 mg 1, 3

For STEMI with fibrinolysis:

• Patients <75 years: 30 mg IV bolus, then 1 mg/kg subcutaneously every 12 hours (max 100 mg for first two doses) 1, 3
• Patients ≥75 years: NO IV bolus, start with 0.75 mg/kg subcutaneously every 12 hours (max 75 mg for first two doses) 1, 2, 3

For primary PCI:

• 0.5 mg/kg IV bolus 1

For VTE treatment:

• 1 mg/kg subcutaneously every 12 hours OR 1.5 mg/kg once daily 1

Step 2: Apply Age-Based Adjustments

• Age <75 years: Use standard weight-based dosing 1, 2
• Age ≥75 years: Reduce to 0.75 mg/kg every 12 hours AND omit initial IV bolus 1, 2, 3

Step 3: Apply Renal Function Adjustments

Calculate creatinine clearance first:

• CrCl ≥30 mL/min: No adjustment needed 1, 2
• CrCl <30 mL/min: Reduce to 1 mg/kg every 24 hours (once daily instead of twice daily) 1, 2, 3

Step 4: Apply Weight-Based Adjustments

For obesity (BMI ≥40 kg/m²):

• Consider reducing intensity to 0.8 mg/kg every 12 hours after first month for VTE treatment 1
• For prophylaxis: 0.5 mg/kg twice daily 2

For low body weight (<60 kg):

• Standard weight-based dosing applies, but monitor closely for bleeding 2

Prophylaxis Dosing

For hospitalized medical patients:

• 40 mg subcutaneously once daily 1, 4

For surgical patients:

• 40 mg subcutaneously once daily, starting 2-4 hours preoperatively or 10-12 hours preoperatively 1

For outpatient cancer patients:

• 40 mg subcutaneously once daily 1

Practical Dosing Examples

Example 1: 70 kg patient with NSTEMI, age 60, normal renal function:

• 30 mg IV bolus immediately
• Then 70 mg (1 mg/kg) subcutaneously every 12 hours 1

Example 2: 80 kg patient with STEMI, age 78, CrCl 45 mL/min:

• NO IV bolus (age ≥75)
• 60 mg (0.75 mg/kg) subcutaneously every 12 hours 1, 2

Example 3: 90 kg patient with DVT, age 55, CrCl 25 mL/min:

• 90 mg (1 mg/kg) subcutaneously every 24 hours (once daily due to renal impairment) 1, 2

Example 4: 120 kg obese patient with PE, age 45, normal renal function:

• First month: 120 mg (1 mg/kg) every 12 hours
• After first month: Consider 96 mg (0.8 mg/kg) every 12 hours 1

Critical Timing Considerations

• Initiate within 24-36 hours of ICU admission for prophylaxis 2
• For trauma patients: Start within 36 hours of injury 2
• For spinal anesthesia: Delay until 8 hours after epidural catheter removal 2
• For PCI patients already on subcutaneous enoxaparin: If last dose was 8-12 hours prior, give additional 0.3 mg/kg IV 2

Common Pitfalls to Avoid

• Never exceed 100 mg for the first two subcutaneous doses in patients <75 years 1, 3
• Never give IV bolus to patients ≥75 years with STEMI 1, 2
• Never use twice-daily dosing in severe renal impairment (CrCl <30 mL/min) 1, 2
• Avoid switching between enoxaparin and UFH due to increased bleeding risk 2
• Do not dose based on total body weight in morbidly obese patients without considering dose reduction after initial treatment 1