sodium phenylbutyrate: clinical use

Prescribing considerations

• Treatment requires supervision by a clinician experienced in urea cycle disorders and coordinated nutritional management.
• Not appropriate as sole management of acute hyperammonaemia.
• Consider the substantial sodium content in heart failure, severe renal impairment, oedema, sodium retention or a low-sodium diet.
• Use cautiously in hepatic or renal impairment because metabolism and elimination involve both organs.
• Review formulation-specific excipients, swallowing ability and enteral access.

Contraindications and cautions

• Hypersensitivity to the active substance or formulation excipients.
• Pregnancy and breastfeeding for all selected products.
• Do not use tablets in dysphagia because delayed oesophageal transit may cause ulceration.
• Granules are unsuitable in fructose intolerance, glucose-galactose malabsorption or sucrase-isomaltase insufficiency because they contain sucrose.

Monitoring

• Plasma ammonia and glutamine, interpreted with clinical status and dietary intake.
• Arginine, essential amino acids—particularly branched-chain amino acids—carnitine and serum proteins.
• Serum potassium because urinary phenylacetylglutamine loss may increase potassium loss.
• Renal and hepatic function, acid-base status and relevant haematology or biochemical abnormalities.
• Adherence, tolerability, nutritional status and signs of acute metabolic decompensation.

Clinical pharmacology

Sodium phenylbutyrate is a prodrug rapidly converted to phenylacetate. Phenylacetate conjugates with glutamine to form renally excreted phenylacetylglutamine, carrying two nitrogen atoms per molecule and bypassing the defective urea-cycle route.

Formulation and product differences

• Tablets are intended for adults and children able to swallow them and contain a clinically relevant sodium load.
• Taste-masked granules contain sodium and sucrose; they may be mixed with suitable drinks or soft food but dissolve slowly and are unsuitable for feeding tubes.
• The oral solution contains sodium and aspartame and is supplied with an oral syringe and optional flavour toppings; it is suitable for compatible nasogastric or gastrostomy tubes.
• The blackcurrant flavour topping for the oral solution contains propylene glycol, requiring particular consideration in very young infants.

Oral solution

Route: Oral

Strengths: 350 mg/mL

Tablet

Route: Oral

Strengths: 500 mg