Patient adherence to warfarin therapy and its impact on anticoagulation control

Warfarin is a commonly prescribed oral anticoagulant in Saudi Arabia and yet patient adherence to warfarin therapy and its impact on anticoagulation control have not been well researched here. A cross-sectional survey was conducted over 6 weeks at the outpatient anticoagulant clinic on patients who were receiving warfarin. Adherence was assessed using the translated Arabic version of the Morisky Medication Adherence Scale (MMAS-8). Levels of adherence were classed as low (score ⩽ 7), or high (score = 8) based on the scores. Good anticoagulation control was defined as percent Time INR in Therapeutic Range (TTR) ⩾ 75% using the Rosendaal method. A total of 192 patients completed a questionnaire with a response rate of 68.1%. It was established that no association was found between adherence to warfarin therapy and INR control groups. Among the 89 (46.4%) patients who had high adherence, only 34 (38.2%) had an acceptable INR control. This was versus 103 (53.6%) patients who had low adherence but also 34 (33.0%) had good INR control. Multivariate logistic regression (MLR) analysis showed that when studying females and occupational status of unemployment, they were independently associated with poor INR control with an OR 2.31, 95% CI 1.10–4.92, and OR 2.71, 95% CI 1.12–6.61 respectively. MLR analysis also showed that age <50 years alongside no formal education was independently associated with low adherence to warfarin therapy with an OR 2.67, 95% CI 1.29–5.52 and OR 2.63, 95% CI 1.01–6.93 respectively. The demographic background influences adherence and INR control, but no association was found between adherence and anticoagulation control.