Identification and Characterization of Perampanel Degradation Products: Stability-Indicating HPLC and In Silico Toxicological Assessment

A stability-indicating HPLC-UV method enabling the simultaneous separation and monitoring of perampanel (PER) and all degradation products was developed and applied, providing adequate resolution and peak purity. Forced degradation studies were conducted to define the degradation profile of PER under acidic, alkaline, oxidative, photolytic, and metal-ion stress conditions. Five degradation products (DP-1 to DP-5) were identified by HPLC–UV and structurally characterized by HRMS/MS, and 1D/2D NMR spectroscopy (1H, 13C, COSY, and HSQC). Acidic hydrolysis produced a benzamide derivative (DP-1) and a benzoic acid derivative (DP-2), oxidative stress generated a pyridine N-oxide derivative (DP-3), and alkaline conditions yielded two previously unreported products, a ring-cleavage derivative of perampanel (DP-4) and a hydroxylated pyridone derivative of perampanel (DP-5). DP-1 was also detected during accelerated stability studies of PER tablets formulated with acidic excipients, demonstrating excipient–drug incompatibility under stressed storage conditions (40 °C/75% RH). The toxicity risk of the five degradation products was assessed using complementary in silico approaches (statistical and expert-rule methods) in accordance with ICH M7 guidance. None of the degradation products showed mutagenic concern and were therefore classified as ICH M7 Class 4 or Class 5 impurities. These results expand the structural knowledge of PER degradation products, clarify its main degradation pathways, and provide experimental and toxicological support for formulation development and impurity control.