A comprehensive study to identify and characterize major degradation products of Ivermectin drug substance including its degradation pathways using LC-HRMS and NMR

Ivermectin (IVM) drug substance is a semi-synthetic macrocyclic lactone that exhibits a broad spectrum of activity and high potency towards endo- and ectoparasites. In this study, a comprehensive forced degradation study was carried out on IVM drug substance (under the conditions recommended in the ICH guidelines) to identify and characterize its major degradation products (DPs). IVM drug substance was subjected to acidic, alkaline, oxidation (H2O2 and K2Cr2O7), thermal (solid and solution state), and photolytic (solid and solution state) stress degradations. Chromatographic separation of the drug substance and its DPs was achieved using a gradient elution on a HALO C18 column (150 × 4.6 mm, 2.7 µm). A total of five major DPs were observed for IVM drug substance under various stressed conditions. Additionally, ivermectin API lots exhibited instability when stored under room temperature and at 45% relative humidity for two years. These DPs were identified and characterized using liquid chromatography-high resolution mass spectrometry (LC-HRMS) and a comparison of their fragmentation profile with IVM H2B1a using tandem mass spectrometry. Of these, H2O2 induced oxidative degradation product (3,4-epoxide H2B1a) was isolated using semi-preparative HPLC and its structure was elucidated comprehensively using LC-HRMS and nuclear magnetic resonance spectroscopy. The proposed structures of the DPs have been rationalized by appropriate degradation pathways of IVM H2B1a. Comprehensive degradation profile of IVM drug substance should facilitate the understanding of the stability profile of IVM drug substance, setting the specification of DPs in finished products as well as aid in the design of generic formulation made with IVM.