Comprehensive study on degradation profile of firocoxib and structural elucidation of its key degradation products

Firocoxib is widely used in veterinary medicine as a non-steroidal analgesic and anti-inflammatory drug substance. Herein, a comprehensive study on the degradation profile of firocoxib was performed through force degradation studies to understand its degradation profile and characterize its major degradation products (DPs). Firocoxib drug substance was subjected to acidic, alkaline, oxidation (H₂O₂, KMnO₄, and K₂Cr₂O₇), thermal (solid and solution state), and photolytic (solid and solution state) stress degradation, as recommended in the ICH guidelines. Firocoxib and its major DPs were adequately separated by investigational HPLC method, which utilized a HALO C18 (100 × 2.1 mm, 2.0 µm) column. Mobile phase-A for the HPLC method is composed of 0.1% formic acid in water and mobile phase-B acetonitrile. A total of six major DPs were observed for firocoxib drug substance under these stress degradation conditions. Structural elucidation of the DPs performed using liquid chromatography-high resolution mass spectrometry and comparison of their fragmentation profile with that of the parent compound. For further structural confirmation of two major DPs, DP-2 and DP-6 were isolated and purified from the stressed samples using a preparative HPLC and analyzed by comprehensive nuclear magnetic resonance (NMR) spectroscopy studies. Most probable mechanistic pathways for the formation of DPs of firocoxib under various stress degradation conditions were postulated to understand its degradation profile. Based on the results from forced degradation, firocoxib was found to be quite stable under basic and thermal conditions, and somewhat unstable under acidic, oxidative, and photolytic conditions. The results of this study should facilitate quality monitoring and establish a stability profile of firocoxib drug substance and drug products. These results may also assist in the design and development of new formulations made with firocoxib drug substance with desired shelf life.