How to manage a patient with an INR of 2.2, which is below the target INR of 3, while on 4 mg of acenocoumarol?

Management of Subtherapeutic INR on Acenocoumarol

Continue the current dose of 4 mg acenocoumarol without adjustment and recheck INR in 1-2 weeks. 1

Rationale for No Dose Change

Your INR of 2.2 falls within the acceptable therapeutic range for a target of 3.0. The ACC/AHA guidelines explicitly state that the acceptable range includes 0.5 INR units on each side of the target, meaning your therapeutic window is 2.5-3.5 for a target of 3.0. 2 However, if your indication is a mechanical mitral valve or you have additional thromboembolic risk factors (atrial fibrillation, previous thromboembolism, hypercoagulable state, or older-generation prosthesis), then an INR of 2.2 is subtherapeutic and requires dose adjustment. 2

Key Decision Point: What is Your Indication?

For Mechanical Aortic Valve WITHOUT Risk Factors:

• Target INR: 2.5 (range 2.0-3.0) 2
• Your INR of 2.2 is therapeutic—no dose adjustment needed 1
• The ACC/AHA guidelines demonstrate that moderate-intensity anticoagulation (INR 2.0-3.0) provides similar thromboembolic protection with lower bleeding risk compared to high-intensity (INR 3.0-4.5) in this population 2

For Mechanical Aortic Valve WITH Risk Factors OR Mechanical Mitral Valve:

• Target INR: 3.0 (range 2.5-3.5) 2
• Your INR of 2.2 is subtherapeutic
• Risk factors include: atrial fibrillation, previous thromboembolism, hypercoagulable state, older-generation prosthesis (ball-in-cage), or severe LV dysfunction 2
• Increase acenocoumarol dose by 10-20% of weekly total (approximately 0.5-1 mg increase per week distributed across dosing days)
• The GELIA study demonstrated that mitral mechanical valve patients with lower INR ranges (2.0-3.5) had lower survival rates than those with higher target ranges (2.5-4.5) 2

Monitoring Strategy

• Recheck INR in 1-2 weeks to confirm stability within therapeutic range 1
• The American College of Chest Physicians recommends against dose adjustments for single INR values ≤0.5 units below target in previously stable patients, as frequent adjustments increase INR variability and worsen outcomes 1
• Once consistently stable, testing frequency can be extended up to 12 weeks, though your stability is not yet established 1

Important Caveats About Acenocoumarol

Acenocoumarol has a shorter half-life than warfarin and may be associated with greater INR instability. 3, 4 Research shows:

• Patients on acenocoumarol have 2-fold higher risk of unstable anticoagulation compared to warfarin 3
• Acenocoumarol users experience 0.3 visits/patient/year with INR ≥6 versus 0.07 with warfarin (p=0.003) 4
• The conversion factor from acenocoumarol to warfarin is approximately 1.8 (meaning 4 mg acenocoumarol ≈ 7.2 mg warfarin) 3

Common Pitfalls to Avoid

• Do not bridge with heparin for a single subtherapeutic INR in stable patients—this is not indicated 1
• Do not supplement with vitamin K in stable patients, as this increases INR variability 1
• Avoid frequent dose adjustments in response to minor INR fluctuations, as this paradoxically worsens control 1
• Be aware of drug interactions: NSAIDs (diclofenac, naproxen, ibuprofen) can increase INR in nearly 50% of acenocoumarol users, with average increases of 1-4 INR units 5
• Antibiotics like amoxicillin can significantly elevate INR on acenocoumarol 6

If Dose Adjustment Is Needed

For patients requiring higher INR (target 3.0, range 2.5-3.5):

• Increase weekly dose by 10-20% (add approximately 3-6 mg to weekly total)
• Distribute the increase across the week (e.g., if taking 4 mg daily = 28 mg/week, increase to 31-33 mg/week)
• Recheck INR in 5-7 days after dose change
• Maintain therapeutic range consistently before extending monitoring intervals 1