Study of Glycerol Phenylbutyrate & Sodium Phenylbutyrate in Phenylbutyrate Naïve Patients With Urea Cycle Disorders

Inclusion Criteria:

- Signed informed consent given by the subject or the subject's parent/legal guardian
for those under 18 years of age or the age of consent by local regulation.

- Male and female subjects with a suspected or confirmed UCD diagnosis of any subtype,
except NAGS deficiency.

- Suspected diagnosis is defined as having experienced a HAC or a documented high
ammonia of >=100 µmol/L

- Confirmed diagnosis is determined via enzymatic, biochemical, or genetic testing.

- Requires nitrogen-binding agents according to the judgment of the Investigator

◦>/= 2 months of age and older.

- All females of childbearing potential and all sexually active males must agree to
use an acceptable method of contraception from signing the informed consent
throughout the study and for 30 days after the last dose of study drug.
Acceptable forms of contraception are (oral, injected, implanted or transdermal),
tubal ligation, intrauterine device, hysterectomy, vasectomy, or double barrier
methods. Abstinence is an acceptable form of birth control, though appropriate
contraception must be used if the subject becomes sexually active.

Exclusion Criteria:

- Subject has received chronic treatment with an oral phenylbutyrate (RAVICTI, NaPBA,
Pheburane, or other) longer than 14 consecutive days within one year prior to
enrollment.

- Temporary use of NaPBA for acute management of a hyperammonemic crisis in the past is
acceptable.

- Any concomitant illness (e.g., malabsorption or clinically significant liver or
bowel disease) which would preclude the subject's safe participation, as judged
by the Investigator.

- Has undergone liver transplantation, including hepatocellular transplant.

- Subjects on NaBz at Baseline will be excluded if they are viewed by the
Investigator as being unable to undergo NaBz transition to a PAA prodrug during
the Initial Treatment Period.

- Known hypersensitivity to PBA or any excipients of the NaPBA/PBA formulations.

- Pregnant or breast-feeding patients. Women of childbearing potential must have a
pregnancy test performed at the Baseline Visit prior to the start of study drug.