Managing a Patient with INR 1.2 on 5mg Coumadin (Warfarin)
The warfarin dose should be increased immediately since an INR of 1.2 is significantly subtherapeutic and places the patient at increased risk of thromboembolism. 1
Assessment of Current Status
An INR of 1.2 while on 5mg of warfarin indicates:
- The patient is significantly below the therapeutic range (typically 2.0-3.0 for most indications)
- The current dose is inadequate to achieve anticoagulation
- The patient has an increased risk of thromboembolism due to subtherapeutic anticoagulation
Management Algorithm
Step 1: Dose Adjustment
- Increase warfarin dose by 20-30% (to approximately 6-6.5mg daily)
- Recheck INR within 3-5 days to assess response
Step 2: Investigate Potential Causes
Look for factors that may contribute to warfarin resistance:
- Poor medication adherence
- Drug interactions that decrease warfarin effect
- Diet high in vitamin K
- Hypermetabolic states (hyperthyroidism)
- Genetic factors affecting warfarin metabolism
Step 3: Follow-up Monitoring
- Once INR approaches therapeutic range, adjust dose as needed
- Monitor INR at least weekly until stable in therapeutic range
- Once stable, monitor INR monthly as recommended by guidelines 1
Target INR Based on Clinical Indication
| Clinical Indication | Target INR | Notes |
|---|---|---|
| Atrial fibrillation | 2.0-3.0 | Standard target for most patients [2] |
| Venous thromboembolism | 2.0-3.0 | For all treatment durations [2] |
| Mechanical heart valves | 2.5-3.5 | For bileaflet/tilting disc valves; higher for caged ball/disc valves [1,3] |
| Post-MI | 2.0-3.0 | With aspirin for high-risk patients [2] |
Special Considerations
Elderly Patients
- More sensitive to warfarin effects
- May require lower doses to achieve therapeutic INR
- Patients ≥75 years typically require 1mg/day less than younger individuals 1
- Consider a narrower target range (2.0-2.5) for elderly patients with atrial fibrillation 3
Drug Interactions
- Check for medications that may decrease warfarin effect:
- Enzyme inducers (rifampin, carbamazepine, phenytoin)
- Vitamin K supplements
- Some antibiotics
- Conversely, be aware that adding certain medications (like acetaminophen at doses >2g/day) can significantly increase INR 4
Dietary Considerations
- Assess for recent changes in vitamin K intake
- Advise consistent intake of vitamin K-containing foods rather than complete avoidance
Common Pitfalls to Avoid
- Overcorrection: Avoid excessive dose increases that may lead to supratherapeutic INR
- Delayed follow-up: Subtherapeutic INR requires prompt reassessment
- Ignoring adherence issues: Always confirm the patient is taking warfarin as prescribed
- Missing drug interactions: Review all medications, including over-the-counter drugs
- Inadequate monitoring: INR should be checked at least weekly during dose adjustments 1
Special Circumstances
Acute Illness
- Acute illnesses (including COVID-19) can affect INR values and warfarin requirements 5
- More frequent monitoring may be needed during illness
- Consider potential drug interactions with medications used to treat the illness
Surgery or Procedures
- For patients requiring procedures, an INR of 1.2 is generally acceptable to proceed without reversal
- After the procedure, resume warfarin at the adjusted higher dose 1
Remember that warfarin dosing must be individualized based on the patient's INR response, and the goal is to maintain the INR within the therapeutic range appropriate for the patient's clinical indication.