Study of Glycerol Phenylbutyrate & Sodium Phenylbutyrate in Phenylbutyrate Naïve Patients with Urea Cycle Disorders (UCDs)

- 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 n-acetylglutamate synthetase (NAGS) deficiency. - Suspected diagnosis is defined as having experienced a hyperammonemic crisis (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 ◦Birth 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.

- 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 sodium benzoate (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 phenylbutyric acid (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.