Management of Subtherapeutic Warfarin
Yes, you can give an additional 5mg of warfarin for one day to a patient who is subtherapeutic on their current 7.5mg dose. This approach is supported by guidelines that recommend dose adjustments for subtherapeutic INR values 1.
Rationale for Dose Adjustment
When managing patients with subtherapeutic INR values on warfarin therapy, the following considerations apply:
- The American College of Chest Physicians guidelines support the use of loading doses to achieve therapeutic anticoagulation more rapidly 1
- A 10mg loading dose has been shown to be safe, with a recurrent VTE rate of only 1.9% and a major bleeding rate of 1.0% at 3 months follow-up 1
- For patients with INR <2.0, increasing the dose by 10-20% is recommended with close monitoring 2
Implementation Approach
- Administer the additional 5mg dose (total 12.5mg for one day)
- Check the INR within 2-3 days to assess response
- Adjust the maintenance dose based on the INR result
- Resume regular dosing schedule after the one-time adjustment
Risk Assessment
The risk of providing this additional dose is minimal compared to the risk of thromboembolism from remaining subtherapeutic. The American Heart Association/American College of Cardiology Foundation notes that even when warfarin is completely stopped for a few days, the risk of thromboembolism is relatively small (0.08-0.16% over 3 days) 1.
Special Considerations
- If the patient has mechanical heart valves or other high-risk conditions, more aggressive correction of subtherapeutic INR may be warranted 1
- For high-risk patients with subtherapeutic INR, therapeutic doses of subcutaneous UFH (15,000 U every 12 h) or LMWH (100 U per kg every 12 h) may be considered during the period of subtherapeutic INR 1
- Monitor for signs of bleeding after dose adjustment
Common Pitfalls to Avoid
- Making too frequent dose changes for INRs only slightly out of range can lead to INR instability 2
- Failing to increase monitoring frequency after dose adjustment can miss potential over-anticoagulation
- Not considering potential drug interactions that may have contributed to the subtherapeutic state
- Overlooking dietary factors (high vitamin K intake) that might be causing resistance to warfarin
After the one-time additional dose, continue to monitor the patient closely and adjust the maintenance dose as needed to maintain the target INR range.