Pharmacodynamics. What is a bioassay or biological assay?

The following pharmacological definition has been taken from the Pharmacology and Experimental Therapeutics Department Glossary at Boston University School of Medicine .

Bioassay or Biological Assay:

“The determination of the potency of a physical, chemical or biological agent, by means of a biological indicator . . . The biological indicators in bioassay are the reactions of living organisms or tissues.” Principles characterizing a bioassay include:

Potency is a property of the material to be measured, e.g., the drug, not a property of the response. Ordinarily, the relationship between changes in behavior of the indicator and differences in drug dose – (a dose-effect curve) – must be determined as a part of each assay.

Potency is relative, not absolute. The potency of one preparation (the “unknown”) can be measured only in relationship to the potency of a second preparation (the “standard” or “reference drug”) that elicits a similar biologic response. When the absolute amounts of standard used in the assay are known, the results of the assay can be used to estimate the amount – in absolute units – of biologically active material contained in the unknown preparation.

A bioassay provides only an estimate of the potency of the unknown; the precision of the estimate should always be determined, using the data of the assay.

(See: Bliss, C.I., American Scientist, 45: 499, 1957).

The copyright of the text is held by Trustees of Boston University. Permission has been granted for its use in this blog.

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