Anticoagulant Clinic Warfarin Adherence Rates and Assessment

Objective: To identify warfarin medication-taking patterns and the relationship between adherence and international normalized ratio (INR). Design: Two-month, single-blind, observational cohort. Setting: Veterans Affairs Medical Center ambulatory care clinics. Patients: Twenty-three veteran outpatients followed in a nurse-managed anticoagulation clinic were enrolled by consecutive sample. Patients were excluded if they used a medication reminder device, were scheduled to have warfarin discontinued within the next 2 months, or had been receiving warfarin less than 1 month. Twenty patients were evaluable. Intervention: All study patients received warfarin in a vial with an electronic medication-event monitoring system (MEMS) device. Patients were not told that adherence was being monitored. Main Outcome Measure: Mean and preclinic warfarin adherence, dosage changes, and INR values were tabulated. Results: Thirty-five percent of the patients were nonadherent with warfarin therapy. Mean and preclinic warfarin adherence rates were 86% and 90%, respectively. Medication-taking behavior was underestimated in 75% of patients. Dosage changes were more common in nonadherent patients. There was not a significant correlation between INR and adherence. Conclusions: MEMS adherence data could have changed pharmacologic management in select patients.