Heparin Dosing for VTE Prophylaxis Based on Weight
For VTE prophylaxis in hospitalized patients, unfractionated heparin 5000 units should be administered subcutaneously every 12 hours for patients weighing less than 100 kg, and every 8 hours for patients weighing 100 kg or more. 1
Evidence-Based Dosing Recommendations
- Unfractionated heparin (UFH) 5000 units subcutaneously every 8 hours is the standard recommended regimen for VTE prophylaxis in hospitalized patients with cancer or high-risk patients 1
- UFH 5000 units subcutaneously every 12 hours has also been used but appears to be less effective, particularly in high-risk patients 1
- For patients weighing more than 100 kg, the more frequent dosing schedule of every 8 hours is recommended to ensure adequate prophylaxis 1, 2
- For patients weighing less than 100 kg without additional risk factors, the every 12 hour dosing regimen is generally sufficient 1, 3
Weight-Based Considerations
Patients ≥100 kg:
- These patients should receive heparin 5000 units subcutaneously every 8 hours 1, 2
- Higher doses (7500 units every 8 hours) have been studied but showed increased bleeding risk without improved efficacy in preventing VTE 2
- The more frequent dosing schedule helps maintain therapeutic levels due to the larger volume of distribution in these patients 1, 2
Patients <100 kg:
- Standard dosing of heparin 5000 units subcutaneously every 12 hours is appropriate 1, 3
- For very low weight patients (≤50 kg), some evidence suggests reduced dosing (heparin 5000 units every 12 hours instead of every 8 hours) may decrease bleeding risk while maintaining efficacy 3, 4
Special Considerations
- Patients with cancer may benefit from the more frequent every 8-hour dosing schedule regardless of weight due to their inherently higher VTE risk 1
- Renal function does not significantly impact UFH dosing as it is primarily cleared through the liver, making it preferable to LMWH in patients with severe renal impairment 1
- Monitoring of aPTT is not routinely required for prophylactic dosing of UFH, unlike with therapeutic dosing 1
Potential Pitfalls
- Using every 12-hour dosing in high-risk or obese patients may lead to subtherapeutic prophylaxis and increased VTE risk 1
- Using every 8-hour dosing in low-weight patients (<50 kg) may increase bleeding risk without additional benefit 3, 4
- Failure to adjust dosing frequency based on weight may lead to either inadequate prophylaxis or increased bleeding complications 2, 3
- In pregnant patients, higher doses of UFH (7500-10000 units every 12 hours) have been associated with elevated aPTT values, which could impact the timing of neuraxial anesthesia 5
Remember that these recommendations are for prophylactic dosing only. Therapeutic dosing for established VTE follows different weight-based protocols 1.