Refill Adherence to Oral Hypoglycemic Agents and Glycemic Control in Veterans

BACKGROUND: Although medication nonadherence may contribute to inadequate diabetes control, adherence is not routinely measured. Persistence, the continuous refill of medications, is one metric that could be integrated into clinical care if associated with glycemic control. OBJECTIVE: To characterize the association of persistence levels (non-, good, overpersistence) with hemoglobin A1c (A1C) over 1 year in newly medicated diabetics in the Veterans Administration. METHODS: Eligible veterans were ≥18 years and first filled a prescription for oral hypoglycemic agents (OHA) between January 1, 2000, and December 31, 2002. The date the OHA was first dispensed was defined as the baseline date. Subjects must have filled at least 1 prescription for any drug, but no diabetes medications, during the 12 months preceding the baseline date. Persistence was measured in days supply of medication over 365 days and defined as non- (1.10) persistence. The main outcome measure was achieving goal A1C (≤7.0%) after 1 year. RESULTS: A total of 56,181 veterans were included. Veterans were male (97%) and white (67%) with comorbid hypertension (58%) and hyperlipidemia (40%). Median age was 63 years, while median baseline A1C was 7.7%. Fifty-two percent of patients had good persistence; 25% were overpersistent. Good persistence was associated with achieving goal A1C (RR 1.07; 95% CI 1.06 to 1.09). The association of overpersistence with the same outcome (RR 0.95; 95% CI 0.94 to 0.97) was lower than good persistence, but higher than nonpersistence (RR 0.93; 95% CI 0.92 to 0.94). CONCLUSIONS: Good persistence was associated with glycemic control. Overpersistent patients were common and more likely than nonpersistent patients, but less likely than good persisters to attain goal A1C. Estimating these different strata of persistence may be useful in identifying patients at risk of poor glycemic control.