Warfarin Dose Adjustment for Subtherapeutic INR
For a patient with an INR of 1.6 (below therapeutic range) on warfarin 2 mg daily, the dose should be increased by 10-20% to 2.5 mg daily. 1
Assessment of Current Anticoagulation Status
Current status:
- INR: 1.6 (subtherapeutic)
- PT: 20.5 seconds
- Current dose: 2 mg daily
Most indications for warfarin therapy require an INR of 2.0-3.0, with a target of 2.5 1, 2
The patient's current INR of 1.6 is below the therapeutic range, increasing risk of thrombotic events
Recommended Dose Adjustment
Primary Recommendation
- Increase warfarin dose by 10-20% to 2.5 mg daily 1
- This modest increase helps avoid overcorrection while moving toward therapeutic range
- Monitor INR within 5-7 days after dose adjustment 1
Rationale for Dose Selection
- Small, incremental dose changes (10-20%) are preferred to avoid INR fluctuations 3
- Loading doses should be avoided as they can cause excessive anticoagulation 3
- The goal is to achieve stable anticoagulation with minimal INR variability, as variability is associated with increased mortality, stroke, and bleeding risk 4
Monitoring Recommendations
- Recheck INR in 5-7 days after dose adjustment 1
- Once stable in therapeutic range, gradually extend monitoring intervals
- Continue frequent monitoring until stable therapeutic range is achieved
Important Considerations
Avoiding Common Pitfalls
- Avoid excessive dose increases that can lead to supratherapeutic INR and bleeding risk
- Avoid loading doses in patients already on warfarin therapy 3
- Consider patient-specific factors that might affect warfarin metabolism (medications, diet, comorbidities)
Special Populations
- For elderly patients (>75 years), consider a lower target INR of 2.0 (range 1.6-2.5) due to increased bleeding risk 1
- For patients with mechanical heart valves, a higher target INR of 2.5-3.5 may be required 2
- For patients on concurrent antiplatelet therapy, more careful monitoring is required due to increased bleeding risk 1
Follow-up Plan
- If INR remains subtherapeutic after dose adjustment, consider additional 10-20% increase
- If INR becomes supratherapeutic (>3.0), reduce dose by 10-20%
- Once stable in therapeutic range for at least 2 consecutive readings, extend monitoring intervals gradually
By implementing this dose adjustment strategy, the patient should achieve therapeutic anticoagulation while minimizing the risk of both thrombotic and bleeding complications.