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Critical reagents play a crucial role in ligand-binding assays; the robustness and reliability of an assay is defined by the quality and long-term availability of these reagents. However, neither regulatory guidelines nor relevant scientific papers provide clear directions for set-up, life cycle management and, more importantly, the acceptance criteria required for the testing of the critical reagents for pharmacokinetic, biomarker and immunogenicity assays. The ambiguity from current guidelines can be a challenge for the bioanalytical community. Members of the European Bioanalysis Forum community undertook a more pragmatic approach on how to assess the impact of critical reagents. In this paper, a review and corresponding gap analysis of the current guidelines and relevant papers will be provided as well as decision trees proposed for lot-to-lot changes of critical reagents for pharmacokinetic assays.

Specific guidelines on bioanalytical method validation for drug development support are recommended by regulatory agencies. Regarding stability assessment, US FDA states that 'Stability procedures should evaluate the stability of the analytes during sample collection and handling, after long-term (frozen at the intended storage temperature) and short-term (bench-top, room temperature) storage, and after going through freeze and thaw cycles and the analytical process'. Additional regulatory considerations are discussed including topics such as analyte and reagent stability. This article reviews the regulatory requirements as issued by the USA (FDA), Europe (EMA) and Japan (MHLW), for stability studies where bioanalytical methods are used to support drug development programs and summarizes the current industry standard for conducting stability studies when utilizing ligand-binding assays.