The Degradation Chemistry of Farglitazar and Elucidation of the Oxidative Degradation Mechanisms

The chemical degradation of farglitazar (1) was investigated using a series of controlled stress testing experiments. Farglitazar drug substance was stressed under acidic, natural pH, basic, and oxidative conditions in solution. In the solid state, the drug substance was stressed with heat, high humidity, and light. Farglitazar was found to be most labile toward oxidative stress. A series of mechanistic experiments are described in which the use of 18O-labelled oxygen demonstrated that oxidative degradation of farglitazar is caused primarily by singlet oxygen formed under thermal conditions. Major degradation products were isolated and fully characterized. Mechanisms for the formation of degradation products are proposed. Drug product tablets were also stressed in the solid state with heat, high humidity, and light. Stressed tablets afforded many of the same degradation products observed during drug substance stress testing, with oxidation again being the predominant degradation pathway. Evidence for the activity of singlet oxygen, formed during thermal stress testing of the solid oral dosage form, is presented. The degradation pathways observed during stress testing matched those observed during long-term stability trials of the drug product.