A group of investigators led by Dr Ralph DeFronzo of the University of Texas Health Science Center in San Antonio, USA, assessed the mechanism by which insulin glargine and rosiglitazone improve glycaemic control when added to treatment with metformin plus sulphonylurea. A total of 20 patients with type 2 diabetes inadequately controlled with metformin plus sulphonylurea received insulin glargine at bedtime or rosiglitazone twice daily for 4 months. Glycaemic control, insulin sensitivity, and glucose production were assessed at baseline and after 4 months.

The investigators found that glycaemic control improved similarly in both treatment groups after 4 months. Endogenous glucose production decreased from baseline in patients who received insulin glargine (p<0.0001) and rosiglitazone (p=0.01). Patients treated with rosiglitazone had a significant reduction in the hepatic insulin resistance index, compared with baseline (p=0.03) and compared with the insulin glargine group (p<0.05), which did not have a significant change from baseline. Rates of glucose disposal increased in both treatment groups, but the increment was greater in the group treated with rosiglitazone (p<0.05).

The investigators concluded that both insulin glargine and rosiglitazone improved glycaemic control by reducing endogenous glucose production, but insulin glargine acted by increasing plasma insulin concentrations, whereas rosiglitazone improved hepatic insulin sensitivity.

Diabetes Care 2006;29:2371-7