Thiazolidinediones are peroxisome-proliferator–activated receptor-γ agonists that increase insulin sensitivity in the peripheral tissues; their FDA approval was largely based on their ability to lower blood glucose levels. Rosiglitazone (Avandia), one of two approved thiazolidinediones, was introduced in 1999 and is used by many patients with diabetes to control blood glucose levels. A third thiazolidinedione, muraglitazar, was not approved for market because of concerns about an increase …