Acenocoumarol Dose Adjustment for Subtherapeutic INR
Increase the weekly acenocoumarol dose by 10-20% (approximately 0.5-1 mg per week total increase) by adjusting the daily regimen to 4 mg daily for 4 days and 3 mg daily for 3 days per week, then recheck INR in 3-5 days. 1
Rationale for Dose Adjustment
Your patient's current regimen of 4 mg and 3 mg on alternate days provides a weekly dose of 24.5 mg (3.5 mg average daily). With an INR of 1.94, which is just below the therapeutic range of 2.0-3.0, a modest dose increase of 10-20% is appropriate rather than aggressive escalation. 2, 1
The American College of Cardiology recommends dose adjustments of 10-20% of the weekly dose when INR is close to but below therapeutic range, as larger adjustments risk overshooting and causing supratherapeutic anticoagulation. 1
A 10-20% increase from 24.5 mg weekly translates to 2.5-5 mg additional per week, which can be achieved by changing the alternating pattern to favor the higher dose more frequently. 1
Specific Dosing Regimen
Recommended adjustment: Change from alternating 4 mg/3 mg to a pattern of 4 mg for 4 days and 3 mg for 3 days per week (total 27 mg weekly, representing a 10% increase). 1
This provides an average daily dose of approximately 3.86 mg, compared to the previous 3.5 mg daily average. 1
Acenocoumarol has a plasma half-life of only 9 hours, significantly shorter than warfarin's 42-hour half-life, meaning dose changes will affect INR more rapidly, typically within 2-3 days. 3
Monitoring Schedule
Check INR in 3-5 days after implementing the dose change, as acenocoumarol's short half-life allows for relatively rapid assessment of dose adequacy. 3
Once INR reaches 2.0-3.0, continue checking twice weekly for 2 weeks to ensure stability, then transition to weekly monitoring for 1 month. 4
The target INR range of 2.0-3.0 applies to most indications including mechanical bileaflet aortic valve replacement without additional risk factors and atrial fibrillation. 2
Critical Considerations for Acenocoumarol
Acenocoumarol requires more frequent monitoring than warfarin due to its shorter half-life, and patients may be more sensitive to dose adjustments. 3, 5
Studies show acenocoumarol is associated with two-fold higher risk for instability of anticoagulation control compared to warfarin, necessitating closer monitoring during dose adjustments. 5
Elderly patients require approximately 20% lower doses of acenocoumarol than younger patients due to increased bleeding risk, so if your patient is elderly, consider the more conservative 10% increase rather than 20%. 4
Alternative Approach if Higher Target Needed
If the patient has a mechanical mitral valve or other indication requiring a target INR of 3.0 (range 2.5-3.5), a larger dose increase of 15-20% would be more appropriate, adjusting to 4 mg for 5 days and 3 mg for 2 days per week (total 29 mg weekly). 2
Common Pitfalls to Avoid
Never continue the current dose hoping INR will drift upward, as an INR of 1.94 indicates inadequate anticoagulation and exposes the patient to thromboembolic risk. 1
Avoid making dose adjustments larger than 20% of the weekly total, as acenocoumarol's pharmacokinetics make patients more sensitive to changes than with warfarin, increasing risk of supratherapeutic INR. 4, 5
Do not use loading doses when adjusting maintenance therapy, as this increases hemorrhagic risk without providing faster achievement of therapeutic range. 3