Assessment of anticoagulation management in outpatients attending a warfarin clinic in Windhoek, Namibia

Background Warfarin, an anticoagulant with a low therapeutic index, requires frequent international normalized ratio (INR) monitoring to ensure efficacy and safety. Little is known about anticoagulation management in Namibia. Objective The purpose of this study was to investigate the level of anticoagulation control among outpatients requiring maintenance warfarin therapy. Setting Clinical records of patients attending the warfarin anticoagulation clinic at Windhoek Central Hospital (Windhoek, Namibia) during a 1-year period were reviewed. Methods Of the 294 outpatients who visited the warfarin anticoagulation monitoring clinic in 2017, 215 patients were included in the data analysis. The following information was available and used for data analysis: age and sex of the patient, indication for warfarin use, number of visits, warfarin dose and INR values. The individual's time in therapeutic range (iTTR) was the primary outcome, which was calculated both using the Rosendaal method and as the percentage of the reported INR values in the therapeutic range. Results The patients' mean iTTR was 29.4%, well below the 65% target, when estimated by the Rosendaal method and 25.2% when calculated as the percentage of INR values within the therapeutic range. Only 22 of the 215 patients (10%) had an iTTR >= 65%. Conclusions Anticoagulation control at this outpatient clinic was low relative to the target iTTR of 65%. Consequently, patients were at risk for further embolic events or bleeding events based on the high numbers of sub- and supratherapeutic INRs during the time period studied.