Pioglitazone, a new thiazolidinedione agent,has been shown to increase insulin sensitivity in clinical trials. Pioglitazone HCI was rapidly absorbed within one hour, achieved peak concentrations at 2-3 h, and was eliminated from serum at 24-36 h. Pioglitazone demonstrated dose-dependent pharmacokinetics. Food did not significantly affect the pharmacokinetic profile of pioglitazone. The pharmacokinetic profile of sulfonylurea agents was not significantly altered by concurrent administration with pioglitazone. Pharmacokinetic studies in healthy volunteers and in patients with type 2 diabetes indicated that pioglitazone may be administered once daily. In patients with type 2 diabetes, pioglitazone as monotherapy and in combination with sulfonylureas or an alpha-glucosidase inhibitor significantly reduced fasting blood glucose, HbA1c, triglycerides, and free fatty acids, and significantly increased HDL-cholesterol. Pioglitazone demonstrated either minor increases or decreases in cholesterol with no adverse effect on LDL-cholesterol. No patients experienced jaundice or ALT elevations > or = three times the upper limit of normal. Adverse events were mild and transient; all subjects returned to their baseline health status or laboratory tests upon withdrawal from, or completion of, the studies. Based upon these preliminary studies, full-scale clinical investigations were conducted in Japan, the United States, and Europe. As a result, in many countries pioglitazone has gained approval for use in patients with type 2 diabetes.