How to increase INR with Coumadin (warfarin)?

How to Increase INR with Warfarin

For patients with subtherapeutic INR on warfarin therapy, increase the weekly dose by 10-15% based on the current INR level and monitor closely until therapeutic range is achieved. 1

Dosing Adjustments Based on INR Values

The European Heart Rhythm Association provides clear guidance on how to increase INR when it falls below therapeutic range:

• For INR < 1.5: Increase warfarin dose by 15% per week 1
• For INR 1.6-1.9: Increase warfarin dose by 10% per week 1
• For INR 2.0-2.9: Maintain current dose (therapeutic range) 1
• For INR 3.0-3.9: Decrease dose by 10% per week 1

Factors Affecting INR Response

Several factors can influence warfarin's effect on INR and should be considered when adjusting dosage:

• Age: Older patients typically require lower doses to achieve therapeutic INR 2
• Medications: Many drugs interact with warfarin and can affect INR:
  • Statins (particularly fluvastatin) can increase INR 1
  • SSRIs may increase INR through CYP450 inhibition 1
  • Carbamazepine and phenytoin decrease INR through enzyme induction 1
• Diet: Consistent vitamin K intake is important for stable INR

Monitoring Protocol After Dose Adjustment

After increasing warfarin dose to raise INR:

• Monitor INR frequently (2-4 times per week) until stable 3
• Once stable, gradually lengthen the interval between INR tests 3
• Avoid excessive dose increases that could lead to supratherapeutic INR and bleeding risk

Special Considerations

• Mechanical heart valves: May require higher target INR (2.5-3.5) 2
• Atrial fibrillation: Standard target INR is 2.0-3.0 2
• Venous thromboembolism: Target INR is typically 2.0-3.0 2

Common Pitfalls to Avoid

• Excessive loading doses: Avoid large loading doses when initiating therapy or increasing dose, as this can lead to excessive anticoagulation 3
• Frequent small adjustments: Making too many small dose changes can lead to poor INR control 4
• Ignoring drug interactions: Many medications can potentiate or inhibit warfarin's effect 1
• Brand switching: Changing between brand-name Coumadin and generic warfarin can cause INR fluctuations and requires closer monitoring 5

Algorithm for Increasing INR

1. Determine current INR value
2. Calculate appropriate dose increase (10-15% weekly dose increase for subtherapeutic INR)
3. Implement new dosing schedule
4. Monitor INR within 5-7 days after dose change
5. Continue adjustments until therapeutic range is achieved
6. Once stable, gradually extend monitoring intervals

Remember that warfarin has a narrow therapeutic window, and dosing must be carefully managed to balance the risks of thromboembolism with bleeding complications. The goal is to maintain the INR within the therapeutic range for as much time as possible.