Troglitazone

Troglitazone is an antidiabetic and anti-inflammatory drug, and a member of the drug class of the thiazolidinediones. It was prescribed for people with diabetes mellitus type 2.[1]

It was patented in 1983 and approved for medical use in 1997.[2] It was subsequently withdrawn.[3]

Mechanism of action

Troglitazone, like the other thiazolidinediones (pioglitazone and rosiglitazone), works by activating peroxisome proliferator-activated receptors (PPARs).

Troglitazone is a ligand to both PPARα and – more strongly – PPARγ. Troglitazone also contains an α-Tocopherol moiety, potentially giving it vitamin E-like activity in addition to its PPAR activation.[4] It has been shown to reduce inflammation.[5] Troglitazone use was associated with a decrease of nuclear factor kappa-B (NF-κB) and a concomitant increase in its inhibitor (IκB). NFκB is an important cellular transcription regulator for the immune response.

History

Troglitazone was developed by Daiichi Sankyo (Japan). In the United States, it was introduced and manufactured by Parke-Davis in the late 1990s but turned out to be associated with an idiosyncratic reaction leading to drug-induced hepatitis. The Food and Drug Administration (FDA) medical officer assigned to evaluate troglitazone, John Gueriguian, did not recommend its approval due to potentially high liver toxicity; Parke-Davis complained to the FDA, and Gueriguian was subsequently removed from his post.[6] A panel of experts approved it in January 1997.[7] Once the prevalence of adverse liver effects became known, troglitazone was withdrawn from the British market in December 1997, from the United States market in 2000, and from the Japanese market soon afterwards. It did not get approval in the rest of Europe.

Troglitazone was developed as the first anti-diabetic drug having a mechanism of action involving the enhancement of insulin resistance. At the time, it was widely believed that such drugs, by addressing the primary metabolic defect associated with Type 2 diabetes, would have numerous benefits including avoiding the risk of

Mechanisms of hepatotoxicity

Since the withdrawal in 2000, mechanisms of troglitazone hepatotoxicity have been extensively studied using a variety of in vivo,[28] in vitro,[29] and computational methods.[30] These studies have suggested that hepatotoxicity of troglitazone results from a combination of metabolic and nonmetabolic factors.[31] The nonmetabolic toxicity is a complex function of drug-protein interactions in the liver and biliary system. Initially, the metabolic toxicity was largely associated with reactive metabolite formation from the thiazolidinedione and chromane rings of troglitazone. Moreover, the formation of quinone and o-quinone methide reactive metabolites were proposed to be formed by metabolic oxidation of the hydroxy group (OH group) of the chromane ring.[28]

Lawsuits

In 2009, Pfizer resolved all but three of 35,000 claims over its withdrawn diabetes drug Rezulin for a total of about $750 million. Pfizer, which acquired rival Wyeth for almost $64 billion, paid about $500 million to settle Rezulin cases consolidated in federal court in New York, according to court filings. The company also paid as much as $250 million to resolve state-court suits. In 2004, it set aside $955 million to end Rezulin cases.[33]

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