Potency is a measure of drug activity expressed in terms of the amount required to produce an effect to given intensity. The more potent a drug the lower the amount required to produce the effect.
The term relative potency is used to express the biological activity of a sample preparation compared to a standard preparation.
In chapter 5.3 of the European Pharmacopoeia 2005 the following definitions for the term potency are given:
- stated potency or labelled potency
In the case of a formulated product a nominal value assigned from knowledge of the potency of the bulk material; in the case of bulk material the potency is estimated by the manufacturer.
- assigned potency
The potency of the standard preparation.
- assumed potency
The provisionally assigned potency of a preparation to be examined which forms the basis of calculating the doses that would be equipotent with the doses to be used of the standard preparation.
- potency ratio
The ratio of equipotent doses of the standard preparation and the unknown preparation under the conditions of the bioassay.
- estimated potency
The potency calculated from bioassay data.