- international unit
1. an internationally agreed upon standard, as measured by bioassay, to which samples of a substance, as a drug or hormone, are compared to ascertain their relative potency.2. the particular quantity of such a substance, which causes a specific biological effect. Abbr.: IU[1920-25]
* * *Any of several precision standards used in measuring physical quantities, such as mass, length, and time (see International System of Units), and also lighting systems, radiation processes, and pharmacology.The luminous intensity or candlepower of a light is expressed in candelas. The second is based on the frequency of radiation emitted by cesium-133 atoms. In radioactive decay, the international unit is the number of disintegrations per second in a sample. In pharmacology, the international unit is the quantity of a substance (vitamin, hormone, or toxin) that produces a specified effect when tested according to an internationally accepted procedure.
* * *▪ unit of measurementin pharmacology, quantity of a substance, such as a vitamin, hormone, or toxin, that produces a specified effect when tested according to an internationally accepted biological procedure. For certain substances, the IU has been identified with a weight of a particular purified form of the material; for example, one gram of vitamin A acetate contains 2.904 × 106 IU. For international units of physical quantities, such as mass, length, etc., see International System of Units.
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