BUPHENYL
Clinical safety rating: caution
Comprehensive clinical and safety monograph for BUPHENYL (BUPHENYL).
BUPHENYL (sodium phenylbutyrate) is a prodrug that is metabolized to phenylacetate. Phenylacetate conjugates with glutamine to form phenylacetylglutamine, which is excreted by the kidneys. This provides an alternative route for waste nitrogen excretion, reducing ammonia levels in patients with urea cycle disorders.
| Metabolism | Sodium phenylbutyrate is rapidly metabolized by beta-oxidation and conjugation to phenylacetate. Phenylacetate is then conjugated with glutamine to form phenylacetylglutamine, which is excreted renally. Minor metabolism via cytochrome P450 enzymes may occur. |
| Excretion | Renal: >80% as phenylacetylglutamine and other conjugates; biliary/fecal: minimal (<5%). |
| Half-life | Terminal half-life: 1.3–5.4 hours (sodium phenylbutyrate); clinically, requires 3–4 times daily dosing to maintain therapeutic levels. |
| Protein binding | Sodium phenylbutyrate: 80–90% bound to albumin; primary metabolite phenylacetate: 70–90% bound. |
| Volume of Distribution | 0.2–0.3 L/kg; suggests distribution primarily in extracellular fluid. |
| Bioavailability | Oral: 100% (sodium phenylbutyrate is rapidly and completely absorbed; prodrug metabolized to phenylacetate). |
| Onset of Action | Oral: 1–2 hours for measurable reduction in plasma ammonia. |
| Duration of Action | Approximately 4–6 hours, requiring multiple daily doses (e.g., 6-hourly in urea cycle disorders). |
4.5-6 g/m²/day orally in 3-4 divided doses; maximum 20 g/day.
| Dosage form | TABLET |
| Renal impairment | Contraindicated in eGFR <30 mL/min/1.73 m². For eGFR 30-59, reduce dose by 50% and monitor ammonia levels. |
| Liver impairment | No specific Child-Pugh adjustments; use with caution in severe hepatic impairment due to risk of ammonia accumulation. |
| Pediatric use | Neonates: 2.5-5 g/m²/day divided every 6-8 hours. Children: 4.5-6 g/m²/day divided every 6 hours. |
| Geriatric use | Start at lower end of dosing range, monitor renal function, and adjust based on creatinine clearance. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for BUPHENYL (BUPHENYL).
| Breastfeeding | Not recommended. No data on M/P ratio; potential for serious adverse reactions in nursing infant. |
| Teratogenic Risk | Animal studies suggest fetal risk; no adequate human studies in first trimester. Risk cannot be excluded in all trimesters. |
| Fetal Monitoring | Monitor maternal ammonia levels, liver function, and amino acid profiles throughout gestation. Fetal ultrasound for growth and anatomical assessment. |
■ FDA Black Box Warning
WARNING: NEUROTOXICITY. Phenylbutyrate and its metabolite phenylacetate may cause neurotoxicity. Use with caution in patients with hepatic or renal impairment, or in those receiving other medications that affect the central nervous system.
| Serious Effects |
Known hypersensitivity to sodium phenylbutyrate or any component of the formulation.
| Precautions | Monitor plasma ammonia levels and ensure dietary protein restriction. Avoid abrupt discontinuation. Use with caution in patients with hepatic or renal impairment, cardiac failure, or conditions requiring sodium restriction. May cause hypernatremia due to sodium content. Monitor for neurotoxicity and interactions with valproic acid or probenecid. |
| Food/Dietary | Must be taken with meals to reduce gastrointestinal effects. High-protein foods should be restricted as part of a low-protein diet for urea cycle disorders. No specific food-drug interactions beyond protein considerations. |
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| Fertility Effects | No human data on fertility impairment; animal studies showed no effect on male or female fertility at clinically relevant doses. |
| Clinical Pearls | BUPHENYL (sodium phenylbutyrate) is used as adjunctive therapy for urea cycle disorders. Monitor plasma ammonia, glutamine, and amino acids. Avoid co-administration with probenecid or NSAIDs which may inhibit renal excretion of phenylacetate. Must be taken with meals to reduce gastrointestinal irritation. Dosing is based on body surface area. Requires monitoring of phenylbutyrate and phenylacetate levels in patients with hepatic impairment. |
| Patient Advice | Take with food and plenty of water to minimize stomach upset. · Do not crush, chew, or open capsules; swallow whole. · Adhere to prescribed low-protein diet as directed by your doctor. · Contact your healthcare provider immediately if you experience vomiting, confusion, or rapid breathing (signs of hyperammonemia). · Avoid use of nonsteroidal anti-inflammatory drugs (NSAIDs) unless approved by your doctor. · Store at room temperature, away from moisture and heat. |