Background: A cohort of patients with type 2 diabetes, prescribed glyburide/metformin tablets, experienced significantly greater improvements in glycaemic control compared to patients receiving glyburide co-administered with metformin.
Aim: To compare the change in A1C for type 2 diabetic patients new to combination therapy with fixed-dose glyburide/metformin tablets vs. glyburide co-administered with metformin in a usual-care setting.
Methods: This retrospective cohort study analysed medication usage via an administrative pharmacy claims database and the patients' corresponding laboratory results. Patients were new to antidiabetic combination therapy with glyburide/metformin tablets or glyburide co-administered with metformin between August 2000 and July 2001 and had A1C measurements at baseline and within 76-194 days of initiating combination therapy. The change from baseline in A1C was analysed using statistical regression to adjust for significant covariates (baseline A1C and dosage). Adherence with therapy was also compared.
Results: The cohort consisted of 950 patients who received glyburide/metformin tablets and 471 taking glyburide co-administered with metformin. Glyburide/metformin patients were younger (mean age = 56 vs. 60 years, p < 0.0001) and received lower doses of each drug than patients taking glyburide co-administered with metformin (glyburide mean final dose = 6 vs. 10 mg/day, p < 0.0001; metformin = 893 vs. 1297 mg/day, p < 0.0001). The mean decrease from baseline A1C, adjusted for baseline A1C and dosage, of 2.02% for glyburide/metformin tablets was significantly (p < 0.0001) greater than the decrease of 1.49% for glyburide co-administered with metformin. Glyburide/metformin patients with baseline A1C >/= 8 experienced a significantly (p < 0.0001) greater decrease in A1C of 2.93% compared to 1.92% for glyburide co-administered with metformin. For patients with baseline A1C < 8%, the difference between the A1C responses remained significant, even though the reductions in A1C were smaller for both glyburide/metformin tablets and glyburide co-administered with metformin (0.54% and 0.23%, p = 0.0017). Patients were more adherent with glyburide/metformin tablets (84% vs. 76%, p < 0.0001), though regression analysis indicated that adherence was not a significant predictor of change in A1C.
Conclusions: The lower medication doses delivered by glyburide/metformin tablets provided a significantly greater reduction in A1C than did glyburide co-administered with metformin in patients with type 2 diabetes, especially when baseline A1C >/= 8%.