Regulatory and scientific considerations in PK and biomarker assay validation: lessons from bioanalytical practice

Bioanalytical method validation is a foundation of drug development, ensuring that pharmacokinetic (PK), toxicokinetic (TK), and biomarker assays produce accurate, precise, reliable, and decision-enabling data. Over the past several decades, advances in analytical technologies including ligand-binding assays (LBAs) and liquid chromatography-tandem mass spectrometry (LC-MS/MS) platforms have transformed the field of bioanalysis. Regulatory guidance from the U.S. Food and Drug Administration (FDA), the European Medicines Agency (EMA), and the International Council for Harmonization (ICH) has evolved to reflect these advancements. This review provides a comprehensive comparison of PK and biomarker assay validation, highlighting critical parameters such as selectivity, sensitivity, calibration, accuracy, precision, dilution/parallelism, specificity, and stability. Best practice recommendations are provided for method development, qualification, and validation, with a focus on fit-for-purpose (FFP) approaches and context-of-use (CoU) considerations. Areas of ambiguity in current regulatory expectations for biomarker validations, common pitfalls encountered during regulatory interactions, and emerging trends in bioanalysis are also reviewed. This review paper aims to guide bioanalytical scientists in developing robust, compliant assays that support regulatory submissions and facilitate informed drug development decisions.