Predictors of Medication-Refill Adherence in an Indigent Rural Population

OBJECTIVE: We evaluated the association of medication refill adherence with demographic and prescription characteristics to determine whether such factors could guide intervention strategies in an indigent rural population. METHODS: The study was conducted at a University-based internal medicine practice serving an indigent rural population. Refill data for diabetes, hypertension, and hypercholesterolemia drugs from a closed pharmacy system were used to calculate mean adherence (for all drugs taken by each patient) and minimum adherence (that of the least adhered to drug) for 1984 patients during a 9-month period. RESULTS: Mean refill adherence was <80% for 33% of the population and minimum refill adherence was <80% for 55% of the patients. Increasing age, race (white), and prescription length were associated with higher mean and minimum adherence, independent of income, prescription copay, and insurance status. Number of drugs taken had a positive mean but negative minimum adherence association. Gender, number of primary care visits, and dosage schedule were not independently associated with adherence. The model explained 6.8% of the variance in mean adherence. CONCLUSIONS: In a rural indigent population, medication refill adherence was associated with race, age, and prescription length, though these factors explained only a small amount of adherence variability. Although ingestion adherence is the goal, refill adherence is a necessary condition for ingestion adherence. To enhance adherence, physicians need better predictors to target their efforts to patients most in need of attention. Prescription claims data could serve this purpose.