Switching from acenocoumarol to warfarin in patients with unstable anticoagulation and its effect on anticoagulation control.

Introduction: Unstable oral anticoagulation increases the risk of thrombotic events and bleedings. Acenocoumarol use has been reported to be associated with two-fold higher risk for instability of anticoagulation control compared to warfarin administration.

Objectives: The aim of the study was to evaluate the effect of introducing warfarin on anticoagulation control in patients with a variable response to acenocoumarol.

Patients And Methods: Sixty-eight subjects treated with acenocoumarol for 5 months or more and displaying intraindividual variability of international normalized ratio (INR) results were switched to warfarin. Unstable anticoagulation was defined as a failure to achieve a target INR within the preceding 3 months, i.e. > or = 50% of 8 or more INR values below 2 or above 3.5. Patients with stable anticoagulation (<20% of out-of-range INRs), matched for age, gender, and anticoagulation indications, served as a reference group.

Results: Patients with unstable anticoagulation on acenocoumarol had higher body mass index (p<0.01) and serum C-reactive protein levels (p<0.01) compared to stable counterparts. The transition factor between acenocoumarol and warfarin was 1.8 (95% CI 1.69-1.96). The percentage time within the target INR range in patients with unstable anticoagulation was 40.2% at baseline and increased to 60.4% following 6 months on warfarin therapy (p<0.05). The number of subjects with <20% of out-of-range INRs among individuals switched from acenocoumarol to warfarin was 22 (32.4%) vs. 63 (92.6%) in patients on stable anticoagulation after 6 months of follow-up (p<0.001).

Conclusions: Switching acenocoumarol to warfarin in patients with unstable anticoagulation can improve anticoagulation control.