Dosing of Unfractionated Heparin in Renal Failure
For patients with renal failure, unfractionated heparin (UFH) is the preferred anticoagulant as it does not require dose adjustment since it undergoes hepatic metabolism rather than renal clearance.
Rationale for UFH in Renal Impairment
UFH is the anticoagulant of choice in patients with severe renal impairment (creatinine clearance < 30 mL/min) for several reasons:
- Unlike low molecular weight heparins (LMWHs) which are primarily eliminated through renal excretion, UFH is predominantly cleared by the reticuloendothelial system in the liver 1
- The American College of Chest Physicians guidelines recommend UFH over LMWH for patients with VTE and severe renal failure (Grade 2C recommendation) 2
- UFH does not accumulate in patients with renal failure, making it safer than LMWHs which can build up and increase bleeding risk 3
Dosing Recommendations for UFH in Renal Failure
Intravenous UFH Dosing
- Initial bolus: 80 U/kg (maximum 4000 U)
- Initial infusion: 18 U/kg/hour (maximum 1000 U/hour) 1
- Target aPTT: 1.5-2.5 times control (approximately 60-80 seconds) 1, 4
aPTT-Based Dose Adjustment Protocol
| aPTT (seconds) | Bolus (U/kg) | Hold (min) | Rate Change | Repeat aPTT |
|---|---|---|---|---|
| < 50 | 50 | 0 | ↑ 10% | 4 hours |
| 50-59 | 0 | 0 | ↑ 10% | 4 hours |
| 60-85 (target) | 0 | 0 | No change | Next day |
| 86-95 | 0 | 0 | ↓ 10% | 4 hours |
| 96-120 | 0 | 30 | ↓ 10% | 4 hours |
| > 120 | 0 | 60 | ↓ 15% | 4 hours |
| [4] |
Subcutaneous UFH Option
For patients with poor IV access or those requiring outpatient therapy:
- Approximately 225-250 U/kg every 12 hours subcutaneously 2
- This approach can be used as a bridge to warfarin therapy
- No routine monitoring required when using fixed-dose subcutaneous regimen 2
Monitoring Considerations
- Monitor aPTT every 6 hours until two consecutive therapeutic values are achieved, then daily 1, 4
- Consider anti-Xa monitoring (target 0.3-0.7 IU/mL) in patients with abnormal baseline coagulation parameters 4, 5
- Check daily complete blood count to monitor for heparin-induced thrombocytopenia (HIT) 4
- Assess for bleeding complications regularly, as renal failure itself increases bleeding risk 3
Special Considerations
- Weight-based dosing is essential for optimal anticoagulation with UFH 1
- Factors affecting UFH response include age, sex, smoking history, and diabetes mellitus 1
- At high doses, some renal clearance of UFH may occur, but this is not clinically significant enough to warrant dose adjustment 1
- For hemodialysis patients, UFH has a terminal half-life of approximately 54 minutes, making it suitable for use during dialysis sessions 6
Advantages of UFH Over Other Anticoagulants in Renal Failure
- Predictable clearance independent of renal function
- Easily reversible with protamine sulfate if bleeding occurs
- Extensive clinical experience in renal failure patients
- No accumulation in patients with severe renal impairment 3
By following these dosing and monitoring recommendations, UFH can be safely and effectively used in patients with renal failure requiring anticoagulation.