Issues in evaluation of bioanalytical method selectivity and drug stability

Evaluation of selectivity is one of the most controversial aspects of method validation and application of methods to studies. The focus of selectivity testing should address the question: Above what level will interference significantly impact on study conclusions? Four key issues will be addressed: the statistical relevance of any selectivity test performed; a criterion for significant interference; experimental methods to establish selectivity; and criteria for acceptance. To ensure that compound integrity is maintained throughout the work-up process, statistically meaningful methods of stability evaluation which are associated with specific acceptance criteria are required. Suitable methods for evaluating stability of analyte and/or solutions of analyte, in process stability, processed sample stability, long term stability and freeze-thaw stability, as well as meaningful acceptance criteria, are presented.