Effects of pioglitazone and rosiglitazone combined with metformin on body weight in people with diabetes

Currently, pioglitazone and rosiglitazone are the thiazolidinediones available for clinical use. In the literature, there are different studies concerning the efficacy, safety and tolerability of thiazolidinediones as add-on therapy to metformin in patients with type 2 diabetes inadequately controlled with metformin alone. Metformin and thiazolidinediones are both antihyperglycaemic drugs, both lower blood glucose concentrations in type 2 diabetes without causing overt hypoglycaemia and both require the presence of insulin to generate their therapeutic effects, but act without stimulating insulin secretion. Some authors reported that the improved glycaemic control obtained with thiazolidinediones is associated with an increase in body weight with an estimated 2-3 kg weight gain for every 1\% decrease in HbA(1c) which could negate some of the benefits of the improved metabolic control. Some other authors, instead, reported that thiazolidinediones give a better improvement in the glycaemic control compared with metformin alone without giving weight gain. The emerging discrepancies from these studies could be because of the study design, the patient selection, the degree of glycaemic control and/or the methods to measure body weight. We have undertaken a thorough literature search on Medline and Embase to evaluate the effects of thiazolidinediones plus metformin combination in people with diabetes on the body weight.