Potency Assay
A test measuring the biological activity of a pharmaceutical product, expressed relative to a reference standard. Potency assays are particularly important for biological peptide products where chemical purity alone may not reflect therapeutic activity. Bioassays or cell-based assays are commonly used.
Technical Context
Potency assays for peptide drugs: (1) bioassays — cell-based functional assays measuring the biological response (e.g. GLP-1R activation assay using cAMP readout for GLP-1 RAs, growth hormone bioassay using Nb2 cell proliferation for somatropin) — most physiologically relevant but higher variability and longer turnaround time; (2) receptor binding assays — competitive binding to the target receptor using radiolabelled or fluorescent ligand — measures binding activity but not downstream signalling; (3) enzyme activity assays — for enzyme-based drugs (e.g. proteasome inhibition assay for bortezomib). Potency is expressed relative to a reference standard in international units (IU) or as percentage of reference. Assay validation parameters (per ICH Q2): specificity, linearity (dose-response range), accuracy, precision (repeatability and intermediate precision), and robustness. For biological products, USP requires lot-by-lot potency testing.