How do you introduce warfarin (International Normalized Ratio (INR) anticoagulant) to a patient currently on a heparin (unfractionated heparin) drip?

Introduction of Warfarin While on Heparin Drip

Warfarin should be initiated on day 1 or 2 of heparin therapy with a starting dose of 5-10 mg daily, while continuing the heparin drip until the INR reaches 2.0-3.0 for at least two consecutive days. 1

Initial Warfarin Dosing

Starting Dose Selection

• For outpatients who are relatively healthy:

  • Start with warfarin 10 mg daily for the first 2 days 1
  • Follow with INR-based dose adjustments

• For inpatients or patients with higher bleeding risk (elderly, malnourished, liver disease):

  • Start with warfarin 5 mg daily 1, 2
  • This approach has a lower risk of anticoagulant overdose 2

Timing of Warfarin Initiation

• Begin warfarin on day 1 or 2 of heparin therapy 1, 3
• Early initiation shortens hospital stay by approximately 4 days compared to delayed initiation 1
• Do not wait several days to start warfarin after beginning heparin 1

Heparin-Warfarin Overlap Management

Duration of Overlap

• Continue full-dose heparin for at least 5 days 1, 3
• Continue heparin until the INR has been in the therapeutic range (2.0-3.0) for at least 2 consecutive days 1, 3
• Do not taper heparin when discontinuing 3

INR Monitoring During Overlap

• Check INR daily during the initial overlap period 1
• Be aware that heparin can falsely elevate INR results with certain thromboplastin reagents 4
  • This effect varies by reagent and can cause errors of 2-55% in INR values
  • Consider checking INR 4-6 hours after temporarily holding heparin if concerned about interference

Expected Timeline

• With 5 mg daily starting dose:

  • Only 21% of patients reach therapeutic INR by day 4
  • About 52% reach therapeutic INR by day 6
  • Most patients take 6-10 days to achieve stable INR 2

• With 10 mg daily starting dose:

  • 83% of patients reach therapeutic INR by day 5
  • Achieves therapeutic INR approximately 1.4 days faster than 5 mg dosing 5

Special Considerations

Monitoring for Complications

• Monitor platelet count during heparin therapy due to risk of heparin-induced thrombocytopenia 1
• Watch for signs of bleeding during the overlap period, as patients are receiving dual anticoagulation

High-Risk Patients

• For patients with high thrombotic risk requiring prolonged warfarin interruption:
  • Restart therapeutic doses of heparin when INR falls below 2.0 6
  • Suspend heparin 4-6 hours before procedures 6
  • Restart as soon as bleeding stability allows 6

Common Pitfalls to Avoid

• Do not discontinue heparin prematurely before therapeutic INR is achieved
• Do not delay warfarin initiation, as this prolongs hospital stay unnecessarily
• Avoid excessive initial warfarin doses in elderly or high-bleeding-risk patients
• Be cautious about INR interpretation during heparin therapy due to potential reagent interference

By following this approach, you can safely transition patients from heparin to warfarin while maintaining effective anticoagulation and minimizing both thrombotic and bleeding risks.