IU (international unit): An international unit (IU) is an internationally accepted amount of a substance. This type of measure is used for the fat-soluble vitamins (such as vitamins A, D and E) and certain hormones, enzymes, and biologicals (such as vaccines).
an amp is a long cylindrical piece of glass that is skinny at one end which you break off to get to the fluid inside. they sometimes come in 2ml dosages but most are 1ml dosages.