Bioassay

Introduction

• Definition — Bioassay (biological assay) is a comparative, quantitative procedure that estimates the relative potency of a test substance against a standard by using a functional response of a living system — animal, isolated tissue, microorganism or cell line — under defined biological conditions.
• Historical origin — The discipline entered formal pharmacopoeial use with Paul Ehrlich's standardisation of diphtheria antitoxin at the close of the 19th century; thereafter bioassay became the routine route to standardising any biological substance of unknown structure.
• Three constituents — Every bioassay has three obligatory elements — stimulus (the test/standard preparation), subject (the animal, tissue or cell system) and response (the measurable functional output).
• Why it matters — Bioassay's distinguishing virtue is greater biological specificity — it isolates the pharmacologically active fraction of a sample; it is irreplaceable for products of unknown structure, natural-origin mixtures and biologicals, where chemical assay alone cannot certify activity.