A Study of the Safety, Efficacy and Pharmacokinetics of Glycerol Phenylbutyrate in Pediatric Subjects Under 2 Years of Age With Urea Cycle Disorders

Inclusion Criteria:

   - Male and female subjects up to 2 years of age

   - Signed informed consent by subject's parent/legal guardian

   - UCD diagnosis or suspected diagnosis of any subtype, except N-acetyl glutamate
   synthetase deficiency. If UCD has not been previously confirmed by genetic testing,
   consent must be obtained from parent/legal guardian prior to perform genetic testing.
   If genetic testing is inconsistent with or excludes a UCD diagnosis, the subject will
   be withdrawn from the study.

Exclusion Criteria:

   - Use of any investigational drug within 30 days of Day 1

   - Uncontrolled infection (viral or bacterial) or any other condition known to
   precipitate hyperammonemic crises. Once these precipitating factors are medically
   controlled, patients presenting in crisis are eligible.

   - Any clinical or laboratory abnormality of Grade 3 or greater severity according to the
   Common Terminology Criteria for Adverse Events (CTCAE) v4.03, except Grade 3
   elevations in ammonia and liver enzymes, defined as levels 5-20 times the upper limit
   of normal in alanine aminotransferase (ALT), aspartate aminotransferase (AST), or
   gamma glutamyl transpeptidase (GGT) in a clinically stable subject

   - Any clinical or laboratory abnormality or medical condition that, at the discretion of
   the Investigator, may put the subject at increased risk by participating in this study

   - Known hypersensitivity to phenylacetate (PAA) or phenylbutyrate (PBA)

   - Liver transplantation, including hepatocellular transplant

   - Subjects on hemodialysis at time of initiating RAVICTI

   - Subjects on RAVICTI for UCD management

   - Currently treated with Carbaglu® (carglumic acid)