Acenocoumarol Dose Adjustment for INR 2.2 with Target 2.5
For a patient with INR 2.2 on acenocoumarol 4 mg daily targeting INR 2.5, continue the current dose unchanged and recheck INR in 1-2 weeks. 1
Rationale for No Dose Adjustment
The current INR of 2.2 falls within the acceptable therapeutic range for a target of 2.5. Guidelines specify that the acceptable range includes 0.5 INR units on each side of the target, meaning your patient's range is 2.0-3.0. 1
A single INR value 0.3 units below target does not warrant dose adjustment. The ACCP guidelines specifically recommend continuing the current dose when a previously stable patient presents with a single out-of-range INR of ≤0.5 units below or above therapeutic. 1
INR fluctuations are normal and expected. Frequent dose adjustments in response to minor INR variations actually increase INR variability, which is associated with worse outcomes including increased complications in patients requiring anticoagulation. 1
Monitoring Strategy
Recheck INR in 1-2 weeks to confirm stability within therapeutic range. 1
For patients with consistently stable INRs, testing frequency can be extended up to 12 weeks, though this patient's stability is not yet established. 1
Avoid bridging with heparin for single subtherapeutic INR values in stable patients, as this is not routinely indicated. 1
Important Caveats
Assess for factors that may have temporarily lowered the INR: recent dietary changes affecting vitamin K intake, new medications (particularly antibiotics like amoxicillin which can interact with acenocoumarol), acute illness, or changes in oral intake. 1, 2
If the patient has a mechanical mitral valve or other high-risk condition, the target INR should be 3.0 (range 2.5-3.5), making this INR of 2.2 genuinely subtherapeutic and requiring dose adjustment. 1
Acenocoumarol has a shorter half-life than warfarin, which can lead to greater INR variability. If this patient demonstrates persistent instability over time, consider switching to a longer-acting vitamin K antagonist like phenprocoumon, though expect a 6-month transition period with initially worse control. 3, 4
Do not routinely supplement with vitamin K in stable patients, as this increases variability. 1