Osmolalities of selected enteral products and carbohydrate modules used to treat inherited metabolic disorders.

Osmolalities of selected defined-formula products for use in treatment of inherited disorders of amino acid metabolism were measured at 12 energy concentrations. Osmotic behaviors of six carbohydrate modules as components of L-amino acid formulas were also studied. Osmolality measurements were made using a Wescor vapor pressure depression osmometer (model 5100 C). Phenyl-Free at concentrations greater than 10 kcal/oz yielded high osmolalities that exceeded the recommended level for infants. Lofenalac, Low Phe/Tyr Diet Powder, and MSUD Diet Powder at concentrations up to but no greater than 20 kcal/oz exerted osmolalities acceptable for use with infants. Low Methionine Diet Powder produced the lowest osmolality of the products tested. Differences among products can be explained by the formulations of the products, with sources of nitrogen and carbohydrate and percents of protein, carbohydrate, and fat considered. Carbohydrate type significantly affected formula osmolality; differences among carbohydrate sources can be attributed to their molecular sizes. Formulas that contained glucose exerted the highest osmolalities, while those with corn syrup or sucrose yielded the next highest. Protein Free Diet Powder, Polycose, and Moducal exerted reasonably low osmolalities.