What is the recommended dosing of enoxaparin (low molecular weight heparin) for patients on warfarin (coumarin) undergoing surgery?

Enoxaparin Dosing for Patients on Warfarin Undergoing Surgery

Enoxaparin dosing for patients on warfarin undergoing surgery should be stratified based on the patient's thromboembolism risk, with prophylactic doses (3000 U SC q12h) for moderate-risk patients and therapeutic doses (100 U/kg SC q12h) for high-risk patients.

Risk Stratification and Perioperative Management

Pre-operative Management

• Stop warfarin 4-5 days before surgery to allow INR to return to normal (≤1.2) 1
• Consider vitamin K 2.5 mg orally 2 days before procedure to reduce the period off anticoagulation 1
• Begin bridging with enoxaparin based on thromboembolism risk 1

Enoxaparin Dosing by Risk Category

Low Thromboembolism Risk (e.g., atrial fibrillation)

• No bridging needed; simply stop warfarin 4-5 days before surgery 1
• Resume warfarin postoperatively at maintenance dose 1
• If necessary, supplement with low-dose enoxaparin (40 mg SC daily) postoperatively 1

Moderate Thromboembolism Risk

• Preoperative: Enoxaparin 3000 U (prophylactic dose) SC every 12 hours 1
• Discontinue enoxaparin 24 hours before surgery 1
• Postoperative: Restart enoxaparin at prophylactic dose 12 hours after surgery 1
• Resume warfarin simultaneously and continue both until INR returns to therapeutic range (4-5 days) 1
• If high bleeding risk postoperatively, delay enoxaparin for 24 hours or longer 1

High Thromboembolism Risk

• Preoperative: Enoxaparin 100 U/kg (therapeutic dose) SC every 12 hours 1
• Discontinue enoxaparin 24 hours before surgery 1
• Postoperative: Restart enoxaparin at prophylactic dose 12 hours after surgery 1
• Resume warfarin simultaneously and continue both until INR returns to therapeutic range 1
• For critical cases requiring continuous anticoagulation: Consider inpatient admission with IV heparin (1300 U/h) stopped 5 hours before surgery 1

Special Considerations

Timing of Postoperative Enoxaparin

• For minor procedures: Resume full therapeutic dose within 24 hours 1
• For major procedures or high bleeding risk: Wait 48-72 hours before resuming full-dose enoxaparin 1
• Consider intermediate-dose enoxaparin regimens (half-therapeutic dose of 1 mg/kg daily) which have shown favorable safety and efficacy profiles 1, 2

Bleeding Risk Management

• For patients at high risk of postoperative bleeding, delay enoxaparin administration for at least 24 hours 1
• If using spinal/epidural anesthesia, avoid enoxaparin administration within 10-12 hours before the procedure to reduce risk of spinal hematoma 3

Important Cautions

• Enoxaparin is not recommended for thromboprophylaxis in patients with prosthetic heart valves 1
• For patients with renal impairment (CrCl <30 mL/min), reduce prophylactic dose to 30 mg SC daily 3
• For obese patients (BMI >30 kg/m²), consider intermediate dosing (40 mg SC q12h) or weight-based dosing 3

Monitoring and Follow-up

• Resume warfarin within 24 hours after surgery at the patient's usual maintenance dose 1
• Continue enoxaparin until the INR returns to the therapeutic range (typically 4-5 days) 1
• Check INR on postoperative day 4 and discontinue enoxaparin when INR >1.9 1