Warfarin Dose Adjustment: 10-15% Increase from 28mg/week
For a patient taking 28mg/week of warfarin, a 10-15% increase translates to 30.8-32.2mg/week (approximately 31-32mg/week), which can be practically implemented as an additional 3-4mg per week distributed across the dosing schedule.
Mathematical Calculation
- 10% increase: 28mg × 1.10 = 30.8mg/week 1
- 15% increase: 28mg × 1.15 = 32.2mg/week 1
- Practical weekly increase: Add 2.8-4.2mg to the total weekly dose 1
Clinical Context for Dose Adjustments
The magnitude of adjustment depends on the clinical scenario:
For Subtherapeutic INR (Below Target Range)
- Most warfarin dose changes should alter the total weekly dose by 5-20%, making a 10-15% increase appropriate for moderately subtherapeutic INR values 1
- A 10-15% increase is reasonable when the INR is consistently below target but not critically low 2
For Thromboembolic Events on Adequate Therapy
- If a patient experiences an embolic event while on warfarin with INR 2.0-3.0, the ACC/AHA guidelines recommend increasing the target INR to 2.5-3.5, which typically requires a larger dose increase than 10-15% 2
- This scenario may necessitate a 20-30% dose increase to achieve the higher target range 2
After Bleeding Episodes
- When restarting warfarin after a bleeding episode is controlled, the weekly dose should be reduced by 10-20% from the previous maintenance dose to avoid recurrent INR elevation 3
- This represents the inverse scenario where dose reduction rather than increase is warranted 3
Practical Implementation Strategies
Weekly Distribution Options for 31-32mg/week:
Option 1 (31mg/week): Increase one day's dose by 0.5mg (if taking 4mg daily × 7 days = 28mg, change to 4mg × 6 days + 4.5mg × 1 day = 28.5mg, then adjust further)
Option 2 (32mg/week): Add 1mg on four days per week (e.g., 4mg × 3 days + 5mg × 4 days = 32mg/week) 1
Monitoring Requirements
- Check INR in 3-5 days after dose adjustment to assess response and ensure movement toward therapeutic range 4
- For patients with previously stable INR who present with a single out-of-range value, the ACCP recommends testing INR within 1-2 weeks 2
- Avoid making dose adjustments for a single slightly out-of-range INR; continue current dose and recheck in 1-2 weeks unless the deviation is significant 2
Important Caveats
- Elderly patients require lower maintenance doses due to altered pharmacokinetics and increased warfarin sensitivity, so a 10-15% increase may produce a greater-than-expected INR response 3
- Patients with hypercoagulable conditions may require approximately 10mg additional total warfarin dose and 2 extra days to reach therapeutic INR compared to standard patients 5
- The correlation between daily warfarin dose and INR is modest (r=0.22), emphasizing the need for individualized monitoring rather than relying solely on dose calculations 6