Transitioning from Warfarin to Therapeutic Heparin Drip
When transitioning from warfarin to a therapeutic heparin drip, discontinue warfarin and initiate full-dose intravenous heparin without delay, with no need to wait for the INR to normalize before starting heparin therapy.
Protocol for Transition
Step 1: Discontinue Warfarin
- Stop warfarin administration immediately
- No need to administer vitamin K to reverse warfarin's effect unless there is active bleeding or an emergent procedure
Step 2: Initiate Therapeutic Heparin Infusion
- Start with an initial bolus of 80 units/kg IV 1
- Follow with a continuous infusion at 18 units/kg/hour 1
- For a 70 kg adult, this translates to approximately:
- 5,600 units IV bolus
- 1,260 units/hour continuous infusion
Step 3: Monitor and Adjust Heparin Therapy
- Check aPTT 4-6 hours after the initial bolus 1
- Adjust the infusion rate to maintain aPTT at 1.5-2.5 times control value (approximately 45-75 seconds) 2
- After any dose change, recheck aPTT in 6-10 hours 2
- Once aPTT is in therapeutic range, monitor daily 2
Important Considerations
Effect of Residual Warfarin on aPTT
- Warfarin affects both INR and aPTT measurements 3
- For each 1.0 increase in INR, the aPTT increases approximately 16 seconds 3
- The effects of warfarin and heparin on aPTT are additive 3
- This may lead to falsely elevated aPTT readings while warfarin is still active in the system
Monitoring Recommendations
- Be aware that initial aPTT values may be elevated due to residual warfarin effect
- Consider measuring both aPTT and anti-Factor Xa levels if available, especially during the first 24-48 hours of transition
- Anti-Factor Xa levels (0.35-0.70) provide a more accurate assessment of heparin activity when warfarin effect is still present 3
Special Patient Populations
- For patients at high risk of thromboembolism (mechanical heart valves, recent thrombosis):
- Ensure no gap in anticoagulation coverage
- Start heparin immediately upon warfarin discontinuation 2
- For elderly patients or those with renal impairment:
- Consider using a lower initial bolus (60 units/kg) and infusion rate (12 units/kg/hour)
- Monitor more frequently for signs of bleeding
Common Pitfalls to Avoid
Waiting for INR to normalize before starting heparin
- This creates a dangerous gap in anticoagulation coverage
- Heparin should be started immediately when transitioning from warfarin
Reducing heparin dose based solely on elevated aPTT during transition
- May result in subtherapeutic heparin levels due to warfarin's effect on aPTT 3
- Consider anti-Factor Xa levels for more accurate heparin dosing during transition
Failing to account for patient-specific factors
- Adjust dosing for extremes of weight, renal function, and bleeding risk
- Higher vigilance needed for patients with recent surgery or procedures
Inadequate monitoring during transition
- The first 24-48 hours require closer monitoring of coagulation parameters
- Watch for signs of bleeding or thrombosis during this period
By following this protocol, you can ensure a safe and effective transition from warfarin to therapeutic heparin while maintaining adequate anticoagulation and minimizing risks of both thrombosis and bleeding.