Factors Affecting Medication Adherence and Anticoagulation Control in Korean Patients Taking Warfarin

BACKGROUND AND RESEARCH OBJECTIVE: Poor adherence in patients taking warfarin may be one of the most common barriers to obtain favorable anticoagulation outcomes. This study was conducted to identify factors affecting medication adherence and their relationships with anticoagulation control in Korean patients taking warfarin. SUBJECTS AND METHODS: In a cross-sectional survey, 204 patients taking warfarin who had visited an outpatient clinic of a cardiovascular center located in Seoul, Korea, were included as research subjects. Medication adherence, knowledge about warfarin, self-efficacy, and patient understanding of the international normalized ratio (INR) were investigated. Participants' medical records were also reviewed to identify clinical characteristics including comorbid conditions, warfarin regimen, and INR. RESULTS AND CONCLUSIONS: When medication adherence was defined as taking warfarin according to medical advice (frequency, dosage, time, and precautions), 56 (27.5%) of 204 respondents were adherent. The adherent group had a greater understanding about warfarin than the nonadherent group as measured by 10 survey items (7.20 ± 1.70 vs 6.56 ± 1.84; P < .05) and had significantly higher self-efficacy (P < .000). However, medication adherence was not associated with good anticoagulation level as measured by INR. The results show that knowledge about warfarin and self-efficacy exert significant influence on medication adherence, and yet medication adherence did not predict therapeutic anticoagulation control. Further studies are needed to identify factors predicting favorable anticoagulation control in patients taking warfarin.