International Unit (IU)

Standard measure of the biological activity (biological effect) of manufactured medicinal drugs and vitamins. For every substance to which this unit is assigned, there is an internationally accepted biological effect expected with a dose of 1 IU. Other quantities of the standard preparation of the substance are expressed in multiples of this dose and may be converted into mass units. For example, 1IU is equivalent to 45.5 microgram (0.0455 milligram) of insulin, 0.6 microgram (0.0006 milligram) of penicillin, 0.3 microgram (0.0003 milligram) of vitamin-A, 50 micrograms (0.050 milligram) of vitamin-C, or 25 nanograms (0.000025 milligram) of vitamin-D.