Sodium phenylbutyrate is a salt of an aromatic fatty acid. The compound is used to treat urea cycle disorders, because its metabolites offer an alternative pathway to the urea cycle to allow excretion of excess nitrogen. Sodium phenylbutyrate is also a histone deacetylase inhibitor and chemical chaperone, leading respectively to research into its use as an anti-cancer agent and in protein misfolding diseases such as cystic fibrosis. It is used as adjunctive therapy for the management of chronic urea cycle disorders due to deficiencies in carbamylphosphate (CPS), ornithine transcarbamylase (OTC), or argininosuccinic acid synthetase. It is indicated in all neonatal- onset efficiency presenting within the first 28 days of life. Also indicated in patients with late-onset, presenting after the first month of life with a history of hyperammonemic encephalopathy. Sodium phenylbutyrate is a pro-drug and is rapidly metabolized to phenylacetate. Phenylacetate is a metabolically active compound that conjugates with glutamine via acetylation to form phenylacetylglutamine. The kidneys then excrete Phenylacetylglutamine. PBA (phenylbutyric acid) is absorbed from the intestine and converted by way of β-oxidation to the active moiety, phenylacetic acid (PAA). PAA is conjugated with glutamine in the liver and kidney by way of N-acyl coenzyme A-l-glutamine N-acyltransferase to form phenylacetylglutamine (PAGN). Like urea, PAGN incorporates two waste nitrogens and is excreted in the urine. On a molar basis, it is comparable to urea (each containing two moles of nitrogen). Therefore, phenylacetylglutamine provides an alternate vehicle for waste nitrogen excretion.

Antineoplaston (Phenylacetylglutamine) is the amino acid acetylation product of phenylacetate (or phenylbutyrate after beta-oxidation). The chemical structure of Antineoplaston AS2-5 corresponds to phenylacetylglutamine. Two synthetic derivatives of Antineoplaston A10 were named Antineoplaston AS2-1 and AS2-5. All antineoplaston formulations were submitted for Phase I clinical studies in advanced cancer patients. The treatment was free from significant side-effects and resulted in objective response in a number of advanced cancer cases. Antineoplastons are an experimental cancer therapy developed by S.R. Burzynski, MD, PhD. Chemically, antineoplastons are a mixture of amino acid derivatives, peptides, and amino acids found in human blood and urine. The developer originally isolated antineoplastons from human blood and later found the same peptides in urine. Urine was subsequently used because it was less expensive and easier to obtain. Since 1980, antineoplastons have been synthesized from commercially available chemicals at the Burzynski Research Institute. According to the developer, antineoplastons are part of a biochemical surveillance system in the body and work as "molecular switches." For the developer, cell differentiation is the key to cancer therapy. At the molecular level, abnormal cells that are potential cancer cells need to be "switched" to normal mode. Antineoplastons are the surveillance system that directs cancer cells into normal channels of differentiation. According to statements published by the developer, people with cancer lack this surveillance system because they do not have an adequate supply of antineoplastons.