International unit
In pharmacology, the international unit (IU) is a unit of measurement for the effect or biological activity of a substance, for the purpose of easier comparison across similar forms of substances. International units are used to quantify vitamins and biologics (hormones, some medications, vaccines, blood products and similar biologically active substances).
International units as used in pharmacology are not part of the International System of Units (SI).[1]
For biologic preparations
Process of definition
To define the IU for a substance, an international collaborative study is organized by the WHO Expert Committee on Biological Standardization using various assay systems in several laboratories.[2] The main goal of the study is to reach a consensus regarding methods of analysis and the approach to standardization so that results can be compared.[3][4][5]
The study is performed using highly purified preparations of the
When a standard sample comes close to depleting, a new standard will have to be found. A new batch of the substance in question is produced and calibrated against the old one, so that the unit still represents the same amount of biological activity. Many substances have undergone several such standard sample changes. The third international standard of prolactin has nearly run out and in 2016 replacement was proposed.[6]
Examples
- 1 IU of rhEGF is defined as the potency of 0.001 μg of a rhEGF in the "91/530" standard vial. One manufacturer reports that its rhEGF is 1.4 times as potent as the 91/530 standard.[7]
- 12.5 IU of oxytocin is defined as the potency of 21 μg of pure peptide in the "76/575" standard vial.[8]
Before the purification of penicillin was perfected, the amounts were also described in "International Units" (and some non-international arbitrary "units" before them) to account for batch-to-batch variation. See Penicillin § Penicillin units.
For vitamins
A number of vitamins have distinct vitamers of distinct biological potencies. There is a system in place also called the international unit to describe the relative strength of these different molecular forms. Like the biological international unit, the IU for vitamins is also an arbitrary number that cannot be interconverted among different types of activities. By 1934, the WHO (then the League of Nations Health Organisation) had already defined the international units for vitamins A, B1, C, and D.[9]
Unlike biologic preparations, small molecules like vitamins can be very easily purified to yield products that are equivalent in potency. As a result, a simple mass conversion (as opposed to an assay) suffices to obtain the IU:
- 1 IU Vitamin A = 0.3 μg retinol (~0.1 nmol) = 0.6 μg beta-carotene[10][11][a]
- 1 IU Vitamin D = 0.025 μg D2/D3 ≈ 0.65 pmol[12]
- 1 IU
History
This section is missing information about what the early biologic standards look like; when did the vitamin A IU receive a conversion for retinol.(December 2023) |
In 1931, the Permanent Commission on Biological Standardisation of the League of Nations Health Organisation specified the provisional standards for vitamins A, B1, C, and D. These original standards were quite crude by modern measures: the standard for vitamin A was a mixture of many carotenoids,
In 1944, officials from the League of Nations, in cooperation with the Royal Society, established a first international standard for penicillin.[14] The postwar World Health Organization established a second standard in 1953. Both were defined using a pure, crystalline substance.[15]
This section is missing information about later standardization of larger biomolecules; bioassays vs immunoassays.(December 2023) |
Languages
The name international unit is often capitalized in English and other languages, although major English-language dictionaries treat it as a common noun and thus use lower case.[1] The name has several accepted abbreviations. It is usually abbreviated as IU in English, and UI in Romance languages (for example Spanish unidad internacional, Portuguese unidade internacional, French unité internationale, Italian unità internazionale, Romanian unitate internațională), IE in several Germanic languages (for example German internationale Einheit, Dutch internationale eenheid) or as other forms (for example Russian МЕ, международная единица [mezhdunarodnaya yedinitsa], Hungarian NE, nemzetközi egység).[citation needed]
In order to remove the possibility of having the letter "I" confused with the digit "1", some hospitals have it as a stated policy omit the "I", that is, to only use U or E when talking and writing about dosages, while other hospitals require the word "units" (or words "international units") to be written out entirely.[16] (For example, "three international units per litre" may be abbreviated "3 U/L". The "liter" sign (L) is less affected, as less confusing written forms are used.)
See also
References
Notes
- ^ The IU/RE equvalency has been replaced by the RAE conversion. See Vitamin A § Equivalencies of retinoids and carotenoids (IU).[10]
- ^ The US NIH has replaced IU with mg d-alpha-tocopherol equiv. See Vitamin E § Food labeling.[10]
Citations
- ^ a b "international unit". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
- ^ PMID 1477965.
- ^ PMID 3048031.
- PMID 1947745.
- PMID 1947747.
- ^ Ferguson, Jackie (2016). "WHO International Collaborative Study of the Proposed 4th International Standard for Prolactin, Human".
- ^ "Unit Conversion Table". R&D Systems.
- ^ "WHO International Standard OXYTOCIN 4th International Standard NIBSC code: 76/575 Instructions for use (Version 4.0, Dated 30/04/2013)" (PDF). nibsc.org.
- ^ doi:10.1038/135516a0.
- ^ a b c d "Unit Conversions". National Institutes of Health. Retrieved 2018-11-21.
- ^ Dietary Reference Intakes Tables: Unit Conversion Factors
- ^ "Vitamin D: Fact Sheet for Health Professionals". Retrieved 6 January 2018.
- .
- ^ PMID 17844083.
- PMID 13082387.
- ^ "Facts about the Official "Do Not Use" List" (PDF). The Joint Commission. Archived from the original (PDF) on March 10, 2013. Retrieved 30 May 2013.
External links
League of Nations archives:
- Sub-sub-series R850-R852/12B/26142 - Standardisation of Biological Products - UN Geneva archives
- Sub-sub-series R6214-R6216/8E/2887 - Permanent Commission on Biological Standardisation - UN Geneva archives
- Bulletin of the Health Organization, volumes 6–11 - National Library of Scotland