Bioassay

Bioassay

1. Definition, scope and historical perspective

• Bioassay is a comparative, quantitative procedure that estimates the relative potency of a test substance against a standard substance by using a functional response of a living system — animal, isolated tissue, microorganism, or cell line — under defined biological conditions (Medhi Ch 2, p.45).
• The discipline traces to the late 18th century and entered formal pharmacopoeial use with Paul Ehrlich's standardisation of diphtheria antitoxin at the close of the 19th century; from then on, bioassay became a routine route to standardising any biological substance whose chemical structure was unknown or whose chemical assay was unavailable (Medhi Ch 2, p.45).
• Etymologically, bio- = living material, assay = laboratory-level estimation; a bioassay is therefore the functional assessment of an unknown substance against a standard, on a living animal or biological tissue, to derive a quantitative dose-response relationship (Medhi Ch 2, p.45).
• A bioassay can be qualitative (records a non-quantifiable physical effect such as deformity or abnormal development) or quantitative (measures concentration / drug dose against a graded or quantal response); MD-level work and pharmacopoeial bioassay are almost always quantitative (Medhi Ch 2, p.45).
• The bioassay has three obligatory constituents — stimulus (the test/standard preparation administered), subject (the animal, isolated tissue, or cell system), and response (the measurable functional output) (Medhi Ch 2, p.45).
• Compared with physical and chemical assays, bioassay's distinguishing virtue is greater biological specificity — it isolates the pharmacologically active fraction of a sample, whereas chemical assay isolates the chemically definable fraction; chemical assay carries greater precision, bioassay greater functional relevance (Medhi Ch 2, p.45).
• For MD Pharmacology, bioassay is the prototype experimental-pharmacology methodology and is examined in RGUHS and NMC competency-based curricula as a postgraduate practical and theory topic (Medhi Ch 2, p.45; Medhi Ch 1).