Knowledge and information levels and adherence to oral anticoagulant therapy with warfarin in patients attending primary health care services

BACKGROUND: Oral anticoagulation therapy with warfarin is widely used around the world and its safety and efficacy are well-established. Nevertheless, anticoagulants are among the drug classes most associated with fatal medication errors in primary health care. OBJECTIVE: To investigate patient knowledge, the level of information provided, and medication adherence in patients treated with warfarin at a primary health care service. METHOD: A cross-sectional study of a prospective cohort of 60 patients on warfarin treatment in the town of Ijuí, Rio Grande do Sul, Brazil. A questionnaire was administered to test patients’ knowledge about their prescriptions and the level of information provided by the health team. The 8-item Morisky Medication Adherence Scale (MMAS-8) and International Normalized Ratio (INR) were used to verify adherence to treatment. RESULTS: The results were expressed in absolute and relative values and prevalence ratios were calculated, with respective 95% confidence intervals. It was found that 83.3% of the participants had been given insufficient information by the health team, 50% did not know how to use the medication correctly, 86.7% were not adherent to the treatment according to MMAS-8 and 63.3% were outside of the correct INR range. CONCLUSION: In this study, we observed a need to improve the quality of information provided to users and to develop strategies to improve adherence to treatment, to ensure the safety of patients treated with warfarin in primary health care services.