Warfarin 5mg Dose Adjustment Based on INR
For patients on established warfarin therapy with INR monitoring, adjust the weekly dose by 10-15% based on INR values using a structured algorithm, maintaining a target INR of 2.0-3.0 for most indications. 1
Dose Adjustment Algorithm for Maintenance Therapy
Use the following systematic approach for dose adjustments based on current INR values:
| INR Value | Action Required | Weekly Dose Change |
|---|---|---|
| <1.5 | Increase dose | +15% per week [1] |
| 1.6-1.9 | Increase dose | +10% per week [1] |
| 2.0-2.9 | Continue current dose | No change (therapeutic range) [1,2] |
| 3.0-3.9 | Decrease dose | -10% per week [1] |
| 4.0-4.9 | Hold 1 dose, then restart | -10% per week [1] |
| ≥5.0 | Hold until INR 2-3 | -15% per week when restarting [1] |
Practical Example for 5mg Daily Dose
- If taking 5mg daily (35mg/week) with INR 1.7: increase to approximately 38.5mg/week (e.g., 5.5mg daily or alternate 5mg/6mg) 1
- If INR 3.5: decrease to approximately 31.5mg/week (e.g., 4.5mg daily) 1
Management of Single Out-of-Range INR Values
For stable patients with a single INR ≤0.5 outside therapeutic range, continue the current maintenance dose without adjustment and retest in 1-2 weeks. 3, 4
- A randomized trial of 160 patients demonstrated no significant difference in follow-up INR between single-dose adjustment versus no adjustment (60% vs 56% in therapeutic range, odds ratio 1.17) 4
- This approach avoids the common pitfall of overreacting to minor fluctuations, which leads to INR instability 1, 3
- More aggressive adjustments are warranted only for persistently low INR or high-risk patients (mechanical heart valves, recurrent thromboembolism) 3
Management of Elevated INR
INR 3.0-4.9 Without Bleeding
- Reduce weekly dose by 10% and continue monitoring 1
- For INR 4.0-4.9: hold one dose, then restart at reduced dose 1
INR 5.0-9.0 Without Bleeding
INR ≥9.0 Without Bleeding
- Give oral vitamin K 3-5mg (expect INR reduction within 24-48 hours) 1
- Avoid high-dose vitamin K (≥10mg) as it causes warfarin resistance for up to one week 1
Life-Threatening Bleeding
- Administer prothrombin complex concentrate plus vitamin K 10mg IV 1
- Fresh frozen plasma is an alternative if prothrombin complex concentrate unavailable 5
INR Monitoring Frequency
The monitoring schedule should be adjusted based on INR stability:
- Daily monitoring until therapeutic INR achieved for 2 consecutive days 1, 2
- 2-3 times weekly for 1-2 weeks after achieving therapeutic range 1
- Weekly for the first month 1
- Every 2-4 weeks once stable 5, 2
- Up to 12 weeks for patients with consistently stable INRs 1, 3
Resume frequent monitoring after any dose adjustment, intercurrent illness, medication changes, or minor bleeding 1
Critical Pitfalls to Avoid
Do not make immediate dose changes for single INR values slightly out of range in previously stable patients. 1, 3, 4 Evidence shows this approach does not improve outcomes and increases INR instability.
Do not use routine heparin bridging for single subtherapeutic INR. 3 A retrospective study of 2,597 patients showed no significant difference in thromboembolic events, while bridging increases bleeding risk 3
Do not stop heparin/LMWH until INR is therapeutic for 2 consecutive days, even if a single reading is in range 6, 2 The overlap must continue for minimum 4-5 days due to delayed warfarin effect 6, 2
Avoid high-dose vitamin K (≥10mg oral) for non-urgent INR reversal, as it causes warfarin resistance 1 Use 3-5mg oral vitamin K for INR ≥9.0 without bleeding 1
Special Considerations
- Drug interactions (NSAIDs, antibiotics, antifungals) require resumed frequent INR monitoring 1, 6
- Vitamin K intake consistency is essential; dietary fluctuations affect warfarin response 1
- Elderly or debilitated patients may require lower maintenance doses (2-5mg daily initially) 2
- Computer-guided dosing algorithms may improve INR control, particularly for inexperienced providers 1, 7