Reclassification of the main impurity (-)-scopolamine hydrobromide trihydrate in scopolamine butylbromide: an integrated ICH M7 guideline assessment combining <i>in silico</i> , <i>in vitro</i> , and <i>in vivo</i> studies

Following the International Council for Harmonisation of Technical Requirements for Pharmaceuticals for Human Use (ICH) multidisciplinary guideline M7 (R2), in silico prediction, in vitro and in vivo genotoxicity evaluations were used to evaluate the potential genotoxic risk of (-)-scopolamine hydrobromide trihydrate (SHT), the main impurity of scopolamine butylbromide in the Chinese Pharmacopoeia (ChP). The 2018 in silico models for genotoxicity (Derek Nexus and Sarah Nexus) predicted SHT to be a Class 4 impurity. Subsequent in vitro and in vivo genotoxicity tests (bacterial reverse mutation test, in vitro mammalian chromosomal aberration test, in vitro mammalian cell gene mutation test and mammalian erythrocyte micronucleus test) showed no positive findings, indicating that SHT has no evidence of genotoxic potential under the tested conditions. Therefore, SHT could be tentatively categorized as a Class 5 impurity according to the ICH multidisciplinary guideline M7 (R2), with a threshold according to ICH quality guideline Q3B (R2). In silico prediction in 2026 confirmed this classification, demonstrating the high reliability of the Nexus software database for classification according to ICH multidisciplinary guideline M7 (R2). In the ChP, the SHT threshold in scopolamine butylbromide falls between the identification thresholds and the qualification thresholds of ICH quality guideline Q3B (R2), which is accurate and reasonable.