Warfarin Time in Therapeutic Range of Primary Healthcare Patients in the Western Cape Province, South Africa

Abstract

Introduction Warfarin therapy is the mainstay of anticoagulation treatment in South Africa and requires frequent INR monitoring due to interindividual patient variability. Time in therapeutic range (TTR) reflects the proportion of total treatment time during which INR values are within therapeutic range. This study determined the TTR for warfarin-treated patients in South African provincial primary healthcare (PHC) facilities over a five-year period. Methods This retrospective cross-sectional analysis used routine data from all patients on warfarin therapy regardless of diagnosis attending PHC facilities in the Western Cape public healthcare sector, from 2018-01-01 to 2022-12-31. TTR, calculated using the Rosendaal method, was assessed using a therapeutic range of 2.0 – 3.0. Adherence was measured using dispensing data. Results Among 20 342 patients on warfarin, TTR could be calculated for 15 371 patients, with 83.2% of patients having suboptimal TTR of ≤ 65.0% and median (IQR) TTR of 37.7% (16.9% – 56.9%). Only 5.0% of patients were classified as adherent and stabilised on warfarin with a median (IQR) TTR of 30.0% (7.7% – 54.2%) in this subset. Younger age, more frequent INR monitoring and more hospital admissions were significantly associated with both adherence itself, and with TTR ≤ 65.0%. Median (IQR) time to first therapeutic INR was 57 (27 – 141) days but was lower when calculated using the Rosendaal method. Conclusion We found suboptimal anticoagulation control in a South African PHC setting which requires strategies for improved patient care. Given the low median TTR, alternatives to warfarin should be considered.