Warfarin Dose Adjustment for INR 3.56
For a patient on warfarin 5 mg daily with an INR of 3.56, reduce the total weekly dose by 10-15% (approximately 3-4.5 mg per week) and recheck the INR in 3-5 days. 1
Immediate Management
- Do not hold warfarin doses for an INR of 3.56 without active bleeding, as this creates unnecessary fluctuations in anticoagulation 1
- Do not administer vitamin K at this INR level—vitamin K is reserved for INR >5.0 without bleeding or any INR with active bleeding 2, 1
- The patient's INR is modestly above the target therapeutic range of 2.0-3.0 but below the threshold requiring aggressive intervention 2, 3
Specific Dose Reduction Strategy
Calculate the Adjustment:
- Current weekly dose: 5 mg × 7 days = 35 mg/week
- 10% reduction: 35 mg × 0.90 = 31.5 mg/week (reduce by 3.5 mg) 1
- 15% reduction: 35 mg × 0.85 = 29.75 mg/week (reduce by 5.25 mg) 1
Practical Implementation:
- Option 1: Reduce to 4.5 mg daily (31.5 mg/week total) 1
- Option 2: Alternate between 5 mg and 4 mg on different days to achieve approximately 30-32 mg/week 4
Monitoring Protocol
- Recheck INR in 3-5 days after implementing the dose reduction 1
- Continue monitoring 2-4 times weekly until the INR stabilizes within the therapeutic range of 2.0-3.0 1
- Once stable, return to monthly monitoring as recommended for stable anticoagulation 2
Clinical Context and Rationale
The bleeding risk increases exponentially when INR exceeds 4.0 and becomes sharply elevated at INR ≥5.0 2, 5. However, at 3.56, the patient remains in a relatively safe zone that requires dose adjustment but not aggressive reversal 2. The American College of Cardiology recommends reducing or omitting the next dose for INR between 3.0-5.0 without bleeding, but more recent structured dosing algorithms favor modest weekly dose reductions (10-15%) rather than holding doses 2, 4, 1.
Critical Pitfalls to Avoid
- Avoid overreacting by holding multiple doses or administering vitamin K, which can cause the INR to drop too low and expose the patient to thrombotic risk 2, 1
- Do not target INR ranges below 2.0, as subtherapeutic anticoagulation (INR <2.0) significantly increases the risk of thromboembolism in patients with AF and DVT history 5, 6
- Assess for contributing factors such as recent dietary changes (vitamin K intake), new medications, illness, or weight changes that may have caused the INR elevation 2, 5
Special Considerations for This Patient
Given the patient's dual indication (AF and DVT history), maintaining therapeutic anticoagulation is critical—both conditions carry high thrombotic risk 2, 3. The target INR remains 2.0-3.0 for both indications 3, 6. For elderly patients (if applicable), consider that they may be more sensitive to warfarin and prone to bleeding even at therapeutic INR levels 1.