Comparative Efficacy of Phenylbutyrate (PBA) vs. Benzoate in Urea Cycle Disorders

The investigators will study and compare how effectively sodium phenylbutyrate, sodium benzoate, and a combination of the two, help excrete nitrogen in healthy volunteers. Subject participation will require three, separate, four-day study periods at least one week apart. During one study period (also called a treatment arm), subjects will take sodium phenylbutyrate; during another they will take sodium benzoate; during another they will take a combination of the two medications. We expect to find that phenylbutyrate is more effective at removing nitrogen than benzoate or a combination of the two.