Sodium Phenylbutyrate

What it is and how it works

Mechanism of Action Sodium phenylbutyrate is a pro-drug and is metabolized to phenylacetate. Phenylacetate is a metabolically-active compound that conjugates with glutamine via acetylation to form phenylacetylglutamine. Phenylacetylglutamine is excreted by the kidneys, hence providing an alternate vehicle for waste nitrogen excretion.

Indications

is indicated as adjunctive therapy to standard of care, which includes dietary management, for the chronic management of adult and pediatric patients with urea cycle disorders (UCDs), involving deficiencies of carbamylphosphate synthetase (CPS), ornithine transcarbamylase (OTC) or argininosuccinic acid synthetase (AS). Limitations of Use Episodes of acute hyperammonemia may occur in patients while on PHEBURANE. PHEBURANE is not indicated for the treatment of acute hyperammonemia, which can be a life-threatening medical emergency that requires rapid acting interventions to reduce plasma ammonia levels. PHEBURANE is a nitrogen-binding agent indicated as adjunctive therapy to standard of care, which includes dietary management, for the chronic management of adult and pediatric patients with urea cycle disorders (UCDs), involving deficiencies of carbamylphosphate synthetase (CPS), ornithine transcarbamylase (OTC) or argininosuccinic acid synthetase (AS). Limitations of Use PHEBURANE is not indicated for the treatment of acute hyperammonemia.

Dosage and administration (summary)

treatment should be supervised by a healthcare provider experienced in the treatment of UCDs. For administration, see full prescribing information. ( 2.1 , 2.4 ) The recommended dosage measured as sodium phenylbutyrate is: Patients weighing < 20 kg: 450–600 mg/kg/day of sodium phenylbutyrate orally. Patients weighing ≥ 20 kg: 9.9–13.0 g/m 2 /day of sodium phenylbutyrate orally. Monitor plasma ammonia levels to determine the need for dosage adjustment. Monitor patients for potential neurotoxicity. For patients with hepatic impairment, start at the lower end of the recommended dosing range.

Contraindications

None None.

Warnings and precautions

Neurotoxicity of Phenylacetate : Increased exposure to phenylacetate, the major metabolite of PHEBURANE, may be associated with neurotoxicity in patients with UCDs. Consider reducing the dose if neurotoxicity symptoms are present. Hypokalemia : Renal excretion of phenylacetylglutamine may induce urinary loss of potassium. Monitor serum potassium during therapy and initiate appropriate treatment when necessary. Conditions Associated with Edema : Calculate the total amount of sodium patients will be exposed to based on their weight or body surface area.

Pregnancy

Pregnancy Risk Summary Available data with sodium phenylbutyrate use in pregnant women are insufficient to identify a drug associated risk of major birth defects, miscarriage or adverse maternal or fetal outcomes. Animal reproduction studies have not been conducted with sodium phenylbutyrate.

Storage and supply

(sodium phenylbutyrate) oral pellets consists of white to off-white pellets and is available in a child-resistant high-density polyethylene (HDPE) bottle with a desiccant in the cap. Each bottle contains 84 g of sodium phenylbutyrate (equivalent to 74 g of phenylbutyrate) in 174 g of oral pellets (NDC 71770-200-10).

Source: Sodium Phenylbutyrate (Pheburane) — US FDA prescribing information, 2026-07-17, DailyMed. Summarised and shortened; the full label governs. Iranian registration, indications and labelling may differ.