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.