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.