Determination of Factors Affecting Time in Therapeutic Range in Patients on Warfarin Therapy

Abstract

Background The effectiveness and safety of warfarin depend on maintaining an international normalized ratio (INR) within the therapeutic range. Time in Therapeutic Range (TTR) is defined as the percentage of time a patient's INR is within the therapeutic range. Objective We sought to determine the factors affecting good TTR in patients on warfarin therapy. Methods This was a descriptive cross-sectional study conducted in a single tertiary care center. Good anticoagulation control was defined as TTR >= 65%. Results The study population consisted of 518 patients. The mean age was 57.6 +/- 12.3 (19-87) and 54.4% of the patients were female. 47.5% patients achieved good anticoagulation control (TTR >= 65%). The mean Medication Adherence Report Scale (MARS) score was significantly higher in patients with good TTR (23.5 +/- 1.9 vs. 22.8 +/- 2.1, p = .002). Only 40.2% of the patients received education on warfarin. In multivariable analyses, the duration of warfarin therapy >10 years (OR: 2.27, 95% CI: 1.34-3.84, p = .002) and MARS score (OR: 1.22, 95% CI: 1.09-1.35, p < .001) were found to be the independent predictors of the good anticoagulation control. Conclusion Duration of warfarin therapy >10 years and MARS score were the independent predictors of good anticoagulation control.