Cystine500 Single Dose Amino Acids, 4 gram packets. 500mg of L-Cystine per 4 gram packet. 15 calories per 4 gram packet. 450 calories per case.A powdered cystine amino acid medical food on a carbohydrate base. For the dietary management of inborn errors of metabolism such as Homocystinuria, and is used under strict medical supervision to provide the specific amounts of cystine unable to be achieved by dietary modification alone. Suitable from 1 year of age.