4-Phenylbutyric acid
Phenylbutyrate and sodium benzoate are orphan drugs approved for the treatment of hyperammonemia in patients with urea cycle disorders, a series of at least 8 rare genetic enzyme deficiencies. The urea cycle is the major pathway of elimination of excess nitrogen including ammonia, and absence of one of the urea cycle enzymes often causes elevations in serum ammonia which can be severe, life-threatening and result in permanent neurologic damage and cognitive deficiencies. Both phenylbutyrate and sodium benzoate act by promoting an alternative pathway of nitrogen elimination. Neither phenylbutyrate nor sodium benzoate have been linked to cases of liver injury either in the form of serum enzyme elevations during therapy or clinically apparent acute liver injury.