PURPOSE: To evaluate the efficacy and tolerability of pioglitazone in combination with a sulfonylurea in the treatment of type 2 diabetes mellitus. SUBJECTS AND METHODS: This 16-week, double-blind study included patients on a stable regimen of a sulfonylurea for greater than or equal to 30 days and with a glycosylated hemoglobin (HbA(1C)) level greater than or equal to8.0%. Patients were randomly assigned to receive once daily pioglitazone 15 mg (n = 184), pioglitazone 30 mg (n = 189), or placebo plus sulfonylurea (n = 187). RESULTS: Patient, receiving pioglitazone + sulfonylurea had significant (P <0.05) decreases from baseline in HbA(1C) and fasting plasma glucose levels compared with patients treated with placebo + sulfonylurea. As compared with placebo, HbA(1C) decreased by 0.9% (95% confidence interval [CI]: 0.06% to 1.2%) with pioglitazone 15 mg and 1.3% (CI: 1% to 1.6%) with 30 mg pioglitazone; fasting plasma glucose levels decreased by 39 mg/dL (95% CI: 27 to 52 mg/dL) with pioglitazone 15 mg and by 58 mg/dL (95% Cl: 46-70 mg/dL) with 30 mg pioglitazone. Both pioglitazone + sulfonylurea groups had significant (P <0.05) mean percent decreases in triglyceride levels (17%, 95% CI: 6% to 27% for 15 mg; 26%,95% CI: 16% to 36% for 30 mg) and increases in high-density lipoprotein cholesterol levels (6%,95% CI: 1% to 11% for 15 mg, 13%, CI: 8% to 18% for 30 mg) compared with placebo + sulfonylurea. There were small but statistically significant mean percent increases in low-density lipoprotein cholesterol levels in all groups. Pioglitazone was well tolerated, and the rates of adverse events were similar in all groups. CONCLUSION: In patients with type 2 diabetes, pioglitazone plus sulfonylurea significantly improves HbA(1C) and fasting plasma glucose levels with beneficial effects on serum triglyceride and HDL-cholesterol levels. (C) 2001 by Excerpta Medica, Inc.