Relationship of Oral Antihyperglycemic (Sulfonylurea or Metformin) Medication Adherence and Hemoglobin A1c Goal Attainment for HMO Patients Enrolled in a Diabetes Disease Management Program

BACKGROUND: There is limited information in the primary literature regarding the relationship of medication adherence to attainment of glycosylated hemoglobin A1c (A1c) goals. The 2 oral antihyperglycemic medications, sulfonylurea and/or metformin, were chosen for retrospective analysis because they are the 2 most common oral medications used by patients with diabetes. OBJECTIVES: To describe the relationship between adherence with 1 or both of 2 oral antihyperglycemic medications (sulfonylurea and metformin) and A1c goal attainment for health maintenance organization (HMO) patients enrolled in a diabetes disease management program. METHODS: This was a retrospective, descriptive evaluation of patients enrolled in a managed care diabetes disease management program in a 188,000-member independent practice association model HMO located in the Southeast. The dataset in this analysis contained demographic, enrollment, pharmacy claims, and clinical laboratory data. Continuously enrolled patients were included if there was a documented A1c value obtained at least 90 days after the initial oral antihyperglycemic medication (sulfonylurea or metformin) prescription index date. The medication possession ratio (MPR) was calculated from the pharmacy claim records and correlated with the A1c value. RESULTS: A total of 42% of patients on sulfonylurea therapy and 46% of those on metformin reached an A1c goal of d7.0%. For patients taking a sulfonylurea, the mean MPR for those who reached the predetermined A1c goal (d7.0) was 0.82 (±0.29) compared with 0.72 (±0.31) for those patients who did not reach the A1c target goal (P less than0.001). For patients taking metformin, the mean MPR for those who reached the predetermined A1c goal was 0.77 (±0.3) versus 0.62 (±0.3) for those patients who did not reach the A1c target goal (P less than0.001). A Pearson correlation analysis revealed a positive relationship between the MPR and A1c for sulfonylurea (r =-0.295, P less than0.001) and for metformin (r=-0.285, P less than0.001). For those patients taking both sulfonylurea and metformin, the Pearson correlation analysis showed a positive relationship between the 2 MPRs (r=0.65, P less than0.001). CONCLUSIONS: Medication adherence as measured by the MPR was higher for patients taking a sulfonylurea or metformin who reached the target A1c goal of d7.0% compared with patients taking these drugs who did not reach the target A1c goal.