Effect of sulfonylurea dose escalation on hemoglobin A1c in Veterans Affairs patients with type 2 diabetes

Sulfonylureas are often titrated to maximum doses despite evidence that their efficacy plateaus above half-maximum doses. The aim of this study was to determine the impact of doubling the dose of glyburide and glipizide to high doses on hemoglobin A1c (HbA1c) in Veterans Affairs patients with type 2 diabetes. A retrospective review of 131 patient cases with prescriptions for high-dose glyburide or glipizide from July 1 through December 18, 2008, was conducted. Three dosage groups were examined: glyburide 5 mg twice daily increased to 10 mg twice daily (GLYB), glipizide 5 mg twice daily increased to 10 mg twice daily (GLIPA), and glipizide 10 mg twice daily increased to 20 mg twice daily (GLIPB). Each patient served as his or her own control; HbA1c after at least 75 days on each dose was compared. There was a statistically significant decrease in HbA1c in GLIPA only (mean ± SD 8.0 ± 1.0 vs. 7.6 ± 1.0%, P = 0.03). No significant change in HbA1c was detected in GLYB (8.1 ± 1.1 vs. 8.1 ± 1.3%, P = 0.80) and the evaluation of GLIPB (8.6 ± 1.7 vs. 8.2 ± 1.1%, P = 0.41) was not adequately powered due to the small sample size. In this small retrospective study, increasing glipizide, but not glyburide, from 5 mg to 10 mg twice daily significantly decreased HbA1c in patients with diabetes.