Formulary
Glycerol phenylbutyrate: Indications, Dosing, Side Effects and Interactions
Glycerol phenylbutyrate is a nitrogen-binding agent that provides an alternative vehicle for waste nitrogen excretion.
MedNext Academy | 3 min read
Glycerol phenylbutyrate: Indications, Dosing, Side Effects and Interactions
Glycerol phenylbutyrate is a nitrogen-binding agent that provides an alternative vehicle for waste nitrogen excretion.
Drug action
Glycerol phenylbutyrate is a nitrogen-binding agent that provides an alternative vehicle for waste nitrogen excretion.
Indications and dose
**Urea cycle disorders (specialist use only)**
- **Adult** (By Mouth, Or By Gastrostomy Tube, Or By Nasogastric Tube): (body surface area 1.3 m 2 and above) Initially 8 g/m 2 daily in divided doses, usual maintenance 5.3-12.4 g/m 2 daily in divided doses, each dose should be rounded up to the nearest 0.5 mL and given with each meal. For dose adjustments based on individual requirements-consult product literature.
**Urea cycle disorders (specialist use only) for glycerol phenylbutyrate**
- **Neonate (body surface area up to 1.3 m2)** (By mouth, or by gastrostomy tube, or by nasogastric tube): Initially 9.4 g/m2 daily in divided doses, usual maintenance 5.3-12.4 g/m2 daily in divided doses, each dose should be rounded up to the nearest 0.1 mL and given with each feed. For dose adjustments based on individual requirements-consult product literature.
- **Child 1-23 months (body surface area up to 1.3 m2)** (By mouth, or by gastrostomy tube, or by nasogastric tube): Initially 9.4 g/m2 daily in divided doses, usual maintenance 5.3-12.4 g/m2 daily in divided doses, each dose should be rounded up to the nearest 0.1 mL and given with each meal or feed. For dose adjustments based on individual requirements-consult product literature.
- **Child 2-17 years (body surface area up to 1.3 m2)** (By mouth, or by gastrostomy tube, or by nasogastric tube): Initially 9.4 g/m2 daily in divided doses, usual maintenance 5.3-12.4 g/m2 daily in divided doses, each dose should be rounded up to the nearest 0.5 mL and given with each meal. For dose adjustments based on individual requirements-consult product literature.
- **Child 2-17 years (body surface area 1.3 m2 and above)** (By mouth, or by gastrostomy tube, or by nasogastric tube): Initially 8 g/m2 daily in divided doses, usual maintenance 5.3-12.4 g/m2 daily in divided doses, each dose should be rounded up to the nearest 0.5 mL and given with each meal. For dose adjustments based on individual requirements-consult product literature.
Cautions
Elderly-limited information available; intestinal malabsorption; pancreatic insufficiency
Contraindications
Treatment of acute hyperammonaemia
Side effects
Common or very common Appetite abnormal; constipation; diarrhoea; dizziness; fatigue; food aversion; gastrointestinal discomfort; gastrointestinal disorders; headache; menstrual cycle irregularities; nausea; oral disorders; peripheral oedema; skin reactions; tremor; vomiting Uncommon Akathisia; alopecia; biliary colic; bladder pain; burping; confusion; depressed mood; drowsiness; dry mouth; dysphonia; epistaxis; fever; gastrointestinal infection viral; hot flush; hyperhidrosis; hypoalbuminaemia; hypokalaemia; hypothyroidism; joint swelling; muscle spasms; nasal congestion; oropharyngeal pain; pain; paraesthesia; plantar fasciitis; speech disorder; taste altered; throat irritation; ventricular arrhythmia; weight changes
Interactions
**Other interactions (9):**
- Concomitant use of medicinal products known to inhibit lipase should be given with caution as glycerol phenylbutyrate is hydrolysed by digestive lipase into phenylbutyrate acid and glycerol.
- Glycerol phenylbutyrate and/or its metabolites, PAA and PBA, have been shown to be weak inducers of CYP3A4 enzyme in vivo .
- In vivo exposure to glycerol phenylbutyrate has resulted in decreased systemic exposure to midazolam of approximately 32% and increased exposure to the 1-hydroxy metabolite of midazolam, suggesting...
- The potential for interaction of glycerol phenylbutyrate as a CYP3A4 inducer and those products predominantly metabolised by the CYP3A4 pathway is possible.
- Therefore, therapeutic effects and/or metabolite levels of medicinal products, including some oral contraceptives that are substrates for this enzyme may be reduced and their full effects cannot be...
- Other medicinal products such as corticosteroids, valproic acid, haloperidol and probenecid may have the potential to affect ammonia levels, see section 4.4.
Pregnancy
Manufacturer advises avoid unless essential-toxicity in animal studies.
Breast feeding
Manufacturer advises avoid-no information available.
Hepatic impairment
Manufacturer advises caution (risk of increased exposure). Dose adjustments Manufacturer advises use lowest possible dose-consult product literature.
Renal impairment
Manufacturer advises use with caution in severe impairment-no information available.
Medicinal forms
Clinical governance
**Author:** MedNext Clinical Team. **Clinical reviewer:** Dr Shameer Deen, MBBS, MS, MRCS. **Sources:** BNF, Indian Pharmacopoeia, CIMS India. **Correction:** Report errors at support@mednext.academy.
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