glycerol phenylbutyrate: clinical use

Prescribing considerations

• Initiate and supervise through a clinician experienced in urea cycle disorders.
• Use only as an adjunct to individualised dietary protein restriction and appropriate nutritional supplementation.
• Acute hyperammonaemia requires rapid alternative intervention; maintenance treatment does not prevent every crisis.
• Assess pancreatic insufficiency or intestinal fat malabsorption because activation and absorption may be reduced.
• Review hepatic and renal impairment, intercurrent illness, protein intake and interacting medicines.

Contraindications and cautions

• Hypersensitivity to glycerol phenylbutyrate
• Treatment of acute hyperammonaemia

Monitoring

• Plasma ammonia and clinical features of hyperammonaemia
• Amino-acid profile, glutamine and nutritional adequacy
• Urinary phenylacetylglutamine where useful for assessing adherence and nitrogen coverage
• Plasma phenylacetate, phenylacetylglutamine and their ratio when neurotoxicity or impaired conjugation is suspected
• Closer ammonia monitoring during illness, pancreatic insufficiency, intestinal malabsorption or use of medicines that may raise ammonia

Clinical pharmacology

A lipase-activated prodrug of phenylbutyrate. Phenylbutyrate is converted to phenylacetate, conjugated with glutamine in the liver and kidneys, and excreted as urinary phenylacetylglutamine, carrying waste nitrogen out of the body.

Formulation and product differences

• Clear, colourless to pale-yellow oral liquid with no listed excipients.
• Supplied in a child-resistant glass bottle with an integrated syringe insert; a compatible oral syringe is required.
• Water introduced into the bottle or measuring syringe can degrade the product.
• After opening, discard the bottle and remaining contents after 14 days.

Oral liquid

Route: Oral

Strengths: 1.1 g/mL