When should enoxaparin (low molecular weight heparin) be administered to patients at high risk of thromboembolic events, such as those undergoing major surgery or with a history of deep vein thrombosis or pulmonary embolism?

When to Give Enoxaparin

Enoxaparin should be initiated postoperatively for VTE prophylaxis in surgical patients, with timing and dosing stratified by thrombotic risk level: 40 mg subcutaneously once daily for very high-risk patients (starting 12-24 hours after surgery), 30 mg subcutaneously twice daily for high-risk orthopedic procedures (starting within 24 hours postoperatively), or standard unfractionated heparin dosing for moderate-risk patients. 1, 2

Risk Stratification and Dosing

Very High-Risk Patients

• Enoxaparin 40 mg subcutaneously once daily is indicated for very high-risk surgical patients, including those undergoing major orthopedic surgery (hip/knee arthroplasty), cancer surgery, or patients with multiple VTE risk factors. 1, 2
• For hip arthroplasty specifically, either 30 mg twice daily or 40 mg once daily demonstrates superior efficacy compared to unfractionated heparin, with the 30 mg twice daily regimen showing an 11% DVT rate versus 14% with 40 mg once daily (though this difference was not statistically significant). 3
• Initiate 12-24 hours after surgery once hemostasis is achieved. 2, 3

High-Risk Patients

• Standard unfractionated heparin 5000 units every 8 hours subcutaneously starting after surgery is the baseline recommendation. 1
• Enoxaparin can be substituted at 30 mg twice daily for enhanced efficacy in orthopedic procedures. 3

Moderate-Risk Patients

• Unfractionated heparin 5000 units every 12 hours subcutaneously is typically sufficient. 1
• Enoxaparin shows equivalent efficacy to unfractionated heparin in this population without clear superiority. 4

Duration of Prophylaxis

• Minimum 10-14 days of prophylaxis is required for all surgical patients receiving enoxaparin. 2
• Extended prophylaxis up to 35 days is strongly recommended for hip arthroplasty and other very high-risk procedures. 2
• For cancer patients undergoing surgery, consider extended prophylaxis for 4 weeks. 2
• Selected very high-risk patients should receive post-discharge enoxaparin. 1

Special Dosing Adjustments

Renal Impairment

• For creatinine clearance <30 mL/min, reduce dose to 30 mg subcutaneously once daily. 1, 2
• Avoid enoxaparin entirely if CrCl <15 mL/min; use unfractionated heparin instead. 2

Obesity

• For body weight >150 kg, increase prophylaxis dose to 40 mg subcutaneously every 12 hours. 1, 5

Cancer Patients

• For VTE treatment (not just prophylaxis) in cancer patients: 1 mg/kg twice daily or 1.5 mg/kg once daily subcutaneously. 1
• Extended prophylaxis with LMWH for 4 weeks is recommended. 2

Critical Timing Considerations and Contraindications

Neuraxial Anesthesia

• Hold enoxaparin for 24 hours BEFORE planned epidural or spinal catheter manipulation (insertion or removal). 1, 5
• Resume no earlier than 2 hours AFTER catheter manipulation. 1, 5
• This is a critical safety measure to prevent epidural hematoma. 5

Major Trauma

• Withhold enoxaparin for at least 2-3 days after major trauma. 1, 5
• Resume only after reviewing current patient condition and risk-benefit ratio. 1, 5

High Bleeding Risk

• If bleeding risk is prohibitively high, use mechanical prophylaxis (pneumatic compression devices) alone until pharmacologic prophylaxis becomes safe. 1, 2
• Target 18 hours daily of intermittent pneumatic compression when used. 2

Treatment Dosing (Acute VTE)

When treating established DVT or PE (not prophylaxis):

• 1 mg/kg subcutaneously twice daily OR 1.5 mg/kg once daily. 1, 6
• Both regimens demonstrate equivalent efficacy to dose-adjusted intravenous unfractionated heparin, with recurrent VTE rates of 2.9% (twice daily) and 4.4% (once daily) versus 4.1% with heparin. 6
• Major hemorrhage rates are similar across all regimens (1.3-2.1%). 6

Adjunctive Measures

• Always combine enoxaparin with mechanical prophylaxis (intermittent pneumatic compression) in very high-risk patients. 1, 2
• Encourage early ambulation as part of multimodal prophylaxis. 1, 2
• Continue aspirin (<100 mg daily) if indicated for other conditions, though this increases bleeding risk. 1

Common Pitfalls

• 42-58% of at-risk patients fail to receive appropriate VTE prophylaxis despite clear guidelines. 2
• Inadequate duration of prophylaxis (stopping at hospital discharge for high-risk patients). 2
• Failure to adjust dosing for renal impairment or obesity. 1, 2
• Initiating enoxaparin too close to neuraxial procedures, risking epidural hematoma. 1, 5
• Not screening for heparin-induced thrombocytopenia history before initiating therapy. 1