Medication Summary

Intravenous sodium benzoate, sodium phenylacetate, and arginine are important therapeutic avenues for reduction of blood ammonia levels.

Class Summary

The use of benzoate and phenylacetate is based on the need to provide alternate routes for waste nitrogen disposal. Benzoate is transaminated to form hippuric acid, which is rapidly cleared by the kidney. Phenylacetate is converted to phenylacetyl CoA and then conjugated with glutamine to form phenylacetylglutamine. Each of these pathways results in disposition of 1 and 2 molecules of ammonia, respectively. Phenylbutyrate is more acceptable as a form of oral therapy because of a diminished odor but is not available for intravenous use.

Sodium benzoate and sodium phenylacetate (Ucephan, Ammonul)

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Combines with glycine to form hippurate, which is excreted in urine. One mol of benzoate removes 1 mol of nitrogen. The oral product (Ucephan) and IV product (Ammonul) contain a combination of sodium benzoate (10 g) and sodium phenylacetate (10 g per 100 mL; 100 mg of each/mL).

Sodium phenylbutyrate (Buphenyl)

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Prodrug rapidly converted orally to phenylacetylglutamine, which serves as substitute for urea and is excreted in the urine, carrying 2 mol of nitrogen per mol of phenylacetylglutamine, assisting in clearance of nitrogenous waste.

Arginine (R-Gene 10)

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Provides 1 mol of urea plus 1 mol ornithine per mol of arginine when cleaved by arginase. Pituitary stimulant for the release of human growth hormone (HGH). Often induces pronounced HGH levels in patients with intact pituitary function. Available as 10% injection (100 mg/mL).

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Urea cycle. Compounds that comprise the urea cycle are numbered sequentially, beginning with carbamyl phosphate. At the first step (1), the first waste nitrogen is incorporated into the cycle; also at this step, N-acetylglutamate exerts its regulatory control on the mediating enzyme, carbamyl phosphate synthetase (CPS). Compound 2 is citrulline, the product of condensation between carbamyl phosphate (1) and ornithine (8); the mediating enzyme is ornithine transcarbamylase. Compound 3 is aspartic acid, which is combined with citrulline to form argininosuccinic acid (4); the reaction is mediated by argininosuccinate (ASA) synthetase. Compound 5 is fumaric acid generated in the reaction that converts ASA to arginine (6), which is mediated by ASA lyase.

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