In pharmacology, the International unit (IU, alternatively abbreviated UI, from French unité internationale) is a unit of measurement for the amount of a substance, based on measured biological activity (or effect). It is used for vitamins, hormones, some drugs, vaccines, blood products and similar biologically active substances. Despite its name, the IU is not part of the International System of Units used in physics and chemistry. Pharmacology (in Greek: pharmacon (φάρμακον) meaning drug, and logos (λόγος) meaning science) is the study of how chemical substances interact with living systems. ... It has been suggested that this article or section be merged with Bioactivity. ... Vitamins are nutrients required for essential metabolic reactions in the body [1]. Vitamins can act both as catalysts and participants in the chemical reaction. ... A hormone (from Greek horman - to set in motion) is a chemical messenger from one cell (or group of cells) to another. ... Oral medication A medication is a licenced drug taken to cure or reduce symptoms of an illness or medical condition. ... A vaccine is an antigenic preparation used to produce active immunity to a disease, in order to prevent or ameliorate the effects of infection by any natural or wild strain of the organism. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... Cover of brochure The International System of Units. ...

The precise definition of one IU differs from substance to substance and is established by international agreement. To define an IU of a substance, the Committee on Biological Standardization of the World Health Organization provides a reference preparation of the substance, (arbitrarily) sets the number of IUs contained in that preparation, and specifies a biological procedure to compare other preparations to the reference preparation. The goal here is that different preparations with the same biological effect will contain the same number of IUs. Flag of World Health Organization The World Health Organization (WHO) is a specialized agency of the United Nations, acting as a coordinating authority on international public health, headquartered in Geneva, Switzerland. ...

For some substances, the equivalent mass of one IU is later established, and the IU is then officially abandoned for that substance. However, the unit often remains in use nevertheless, because it is convenient. For example, Vitamin E exists in a number of different forms, all having different biological activities. Rather than specifying the precise type and mass of vitamin E in a preparation, for the purposes of pharmacology it is sufficient to simply specify the number of IUs of vitamin E. Mass is a property of a physical object that quantifies the amount of matter and energy it contains. ... Tocopherol, or Vitamin E, is a fat-soluble vitamin in eight forms that is an important antioxidant. ...

The mass equivalents of 1 IU for selected substances:

• 1 IU Insulin: the biological equivalent of about 45.5 μg pure crystalline insulin (1/22 mg exactly)
• 1 IU Vitamin A: the biological equivalent of 0.3 μg retinol, or of 0.6 μg beta-carotene
• 1 IU Vitamin C: 50 μg ascorbic acid
• 1 IU Vitamin D: the biological equivalent of 0.025 μg cholecalciferol/ergocalciferol (1/40 μg exactly)
• 1 IU Vitamin E: the biological equivalent of about 0.667 mg d-alpha-tocopherol (2/3 mg exactly), or of 1 mg of dl-alpha-tocopherol acetate

The IU should not be confused with the enzyme unit, which is also known as the "International unit of enzyme activity" and is abbreviated as U. The structure of insulin. ... The microgram (symbol µg, sometimes mcg) is an SI unit of mass. ... Retinol, the dietary form of vitamin A, is a fat-soluble, antioxidant vitamin important in vision and bone growth. ... Retinol, the dietary form of vitamin A, is a fat-soluble, antioxidant vitamin important in vision and bone growth. ... Carotene is an orange photosynthetic pigment important for photosynthesis. ... It has been suggested that this article or section be merged into Ascorbic acid. ... This article deals with the molecular aspects of ascorbic acid. ... Vitamin D is a fat soluble vitamin that contributes to the maintenance of normal levels of calcium and phosphorus in the bloodstream. ... Tocopherol, or Vitamin E, is a fat-soluble vitamin in eight forms that is an important antioxidant. ... The milligram (symbol mg) is an SI unit of mass. ... An enzyme unit is the amount of enzyme that catalyzes the transformation of 1 micromole of substance per minute at 30°C. It is commonly used to measure the specific activity of an enzyme. ...

External links

• WHO reference preparations