To evaluate the change in hemoglobin A1C (A1C) in patients with type 2 diabetes switched from coadministration of a sulfonylurea (SU), glyburide or glipizide, and metformin (SU+Met) to a single glyburide-metformin tablet. A retrospective cohort study design of patients with type 2 diabetes treated at 3 Veterans Affairs Medical Centers and 1 Department of Defense Medical Center was utilized. One hundred percent of patients receiving glyburide-metformin tablets were screened for inclusion. Patients with at least 6 months of prior SU+Met combination therapy and a baseline A1C measured within 35 days prior to or 3 days after switch to glyburide-metformin tablets were included. At least one documented follow-up A1C at >or=90 days after the switch to glyburide-metformin was required for inclusion. Glycemic control, complications, lipid parameters, concomitant medications, and weight were analyzed prior to and following the switch to glyburide-metformin. Seventy-two patient records were included after the disqualification criteria excluded 488 prospective patients. The mean age of the 72 patients was 62 years; average body mass index was 32.9 kg/m2, average baseline A1C was 8.3%, and the average time since diagnosis was 7.6 years. The mean reduction in A1C was 0.6% (P=0.002) at a mean follow-up of 196 days after the switch to glyburide-metformin tablets. Improvement in glycemic control was predominantly seen in patients with a baseline A1C >or=8% in whom a 1.3% mean reduction in A1C (P=0.0002) was achieved despite a lower mean final dose of glyburide. The results of this study suggest that in type 2 diabetic patients with an A1C >or=8%, switching from coadministration of a sulfonylurea plus metformin to combination glyburide-metformin tablets may provide an improvement in glycemic control in the range of a 1.2 to 1.4 absolute percentage point decrease in A1C. A randomized, prospective trial comparing these 2 methods of treatment is needed, however, to determine the precise effect provided by the unique formulation of glyburide in the glyburide-metformin tablet.