Quantification of abemaciclib and metabolites: evolution of bioanalytical methods supporting a novel oncolytic agent.

Bioanalytical methods undergo many revisions and modifications throughout drug development to meet the objectives of the study and development program. Validated LC-MS/MS methodology used to quantify abemaciclib and four metabolites in human plasma is described. The method, initially validated to support the first-in-human study, was successfully modified to include additional metabolites as and information about the activity and abundance of human metabolites became available. Consistent performance of the method over time was demonstrated by an incurred sample reanalysis passing rate exceeding 95%, across clinical studies. An overview of the numerous methods involved during the development of abemaciclib, including the quantification of drugs evaluated as combination regimens and used as substrates during drug-drug interaction studies, is presented. Robust bioanalytical methods need to be designed with the flexibility required to support the evolving study objectives associated with registration and post-registration trials.