To assess the efficacy and safety of adding rosiglitazone to an established regimen of glyburide/metformin in patients with type 2 diabetes who had not achieved adequate glycemic control (glycosylated hemoglobin [HbA_1C] levels >7.0% and ≤10.0%).

Following an open-label, lead-in phase to optimize the dosing of glyburide/metformin tablets, 365 patients randomly received additive therapy comprising rosiglitazone (4 mg once daily) or placebo for 24 weeks. Based on glycemic response, rosiglitazone dose was maintained or increased to 4 mg twice daily. Glyburide/metformin dose was maintained or reduced by 2.5/500 mg for symptomatic hypoglycemia. The primary endpoint was the change in HbA_1C level from baseline to week 24. The proportions of patients achieving HbA_1C levels <7% and a fasting plasma glucose level <126 mg/dL were also assessed.

After 24 weeks, therapy with glyburide/metformin plus rosiglitazone resulted in a greater reduction in HbA_1C levels (–1.0%, P <0.001) compared with combination therapy that included placebo, and in a larger proportion of patients (42% vs. 14%) who attained levels <7%. The difference in fasting plasma glucose levels between groups was –48 mg/dL (P <0.001), favoring glyburide/metformin plus rosiglitazone. The adverse event profile in the rosiglitazone-treated group included mild-to-moderate edema (8%), hypoglycemia (22%), and weight gain of 3 kg. No patient experienced hypoglycemia requiring third-party assistance.

In patients with inadequate glycemic control despite established glyburide/metformin therapy, the addition of rosiglitazone improves glycemic control, allowing more patients to achieve an HbA_1C level <7% and perhaps delaying the need for insulin treatment.