PHEBURANE
Clinical safety rating
cautionComprehensive clinical and safety monograph for PHEBURANE (PHEBURANE).
Pheburane (sodium phenylbutyrate) is a prodrug that is metabolized to phenylacetate, which conjugates with glutamine to form phenylacetylglutamine. This alternative pathway for nitrogen excretion reduces ammonia levels in patients with urea cycle disorders.
| Metabolism | Primarily hepatic and renal; hydrolyzed by esterases to phenylacetate; phenylacetate then conjugated with glutamine via acyl-CoA synthetase and acyl-CoA:glutamine N-acyltransferase to form phenylacetylglutamine. |
| Excretion | Primarily renal excretion. Approximately 50-80% of a dose is excreted unchanged in urine via glomerular filtration and tubular secretion. Biliary/fecal elimination is minimal (<5%). |
| Half-life | Terminal elimination half-life is approximately 1-2 hours in patients with normal renal function. In patients with renal impairment, half-life may be prolonged (up to 4-6 hours), necessitating dose adjustment. |
| Protein binding | Approximately 10-20% bound to plasma proteins, primarily albumin. Binding is low and not clinically significant. |
| Volume of Distribution | Volume of distribution is approximately 0.3-0.5 L/kg, indicating distribution primarily in extracellular fluid. Not extensively distributed into tissues. |
| Bioavailability | Oral bioavailability is approximately 80-100% after administration of the sodium phenylbutyrate prodrug. PHEBURANE itself is a prodrug; bioavailability refers to conversion to phenylacetate and then to phenylacetylglutamine. |
| Onset of Action | Oral: Onset of action occurs within 1-2 hours after administration, as reduction in plasma ammonia levels begins. Intravenous: Onset within 15-30 minutes. |
| Duration of Action | Duration of ammonia-lowering effect is approximately 4-6 hours after a single oral dose, corresponding to the drug's half-life. Continuous therapy is required for sustained effect. |
| Molecular Weight | 192.21 |
Adults: 1 gram orally twice daily, increased as tolerated to 2 grams orally twice daily. Maximum dose: 20 grams per day.
| Dosage form | PELLETS |
| Renal impairment | Contraindicated in patients with GFR < 50 mL/min/1.73 m² due to risk of hyperammonemia. |
| Liver impairment | No specific adjustment recommended for Child-Pugh A or B. Use with caution in severe hepatic impairment (Child-Pugh C) due to limited data. |
| Pediatric use | Neonates and children: 4.5 to 5.9 grams/m²/day orally in 2 to 4 divided doses. Doses up to 12.5 grams/day have been used. |
| Geriatric use | No specific adjustments recommended; use with caution due to age-related renal decline. Monitor renal function and ammonia levels. |
| 1st trimester | Insufficient human data; animal studies show no teratogenicity at clinically relevant doses. Use only if clearly needed. |
| 2nd trimester | No known teratogenicity; avoid maternal hyperammonemia as it may harm fetus. Monitor ammonia levels. |
| 3rd trimester | Avoid maternal hyperammonemia; neonatal hyperammonemia has been reported. Use with caution. |
Clinical note
Comprehensive clinical and safety monograph for PHEBURANE (PHEBURANE).
| Placental transfer | Phenylbutyrate and its metabolites cross the placenta; extent unknown but expected due to low molecular weight. |
| Breastfeeding | Excreted into breast milk in low amounts; potential for severe adverse reactions in infant. Manufacturer recommends caution; weigh benefits vs risks. |
| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | Pheburance (sodium phenylbutyrate) has not been studied in pregnant women. In animal studies, phenylbutyrate caused fetal harm at doses equivalent to human therapeutic doses. First trimester: Potential for teratogenicity based on animal data. Second and third trimesters: May cause fetal growth restriction and neurotoxicity due to ammonia-lowering effects. Use only if benefit outweighs risk. |
| Fetal Monitoring | Monitor maternal serum ammonia, serum electrolytes, blood urea nitrogen, liver function, and complete blood count. Fetal monitoring should include serial ultrasound for growth and amniotic fluid volume. Consider fetal echocardiography due to potential cardiac effects. |
| Fertility Effects | No specific studies on fertility in humans. In animal studies, no adverse effects on fertility were observed. However, the underlying metabolic disorder may impact fertility. Men should use effective contraception during therapy due to potential genotoxicity. |
■ FDA Black Box Warning
None
| Serious Effects |
Hypersensitivity to phenylbutyrate or any component
| Precautions | May cause fluid retention and electrolyte abnormalities (e.g., hypernatremia, hypokalemia) due to sodium content, Pancreatitis has been reported, Neurotoxicity with high plasma phenylacetate levels (e.g., somnolence, confusion, seizures), May impair platelet function; caution in bleeding disorders or surgery, Monitor ammonia levels, serum electrolytes, liver function, and complete blood counts regularly |
| Food/Dietary | Avoid high-protein foods as they increase ammonia production. Take with meals to improve tolerability. No known significant food-drug interactions. |
| Clinical Pearls | PHEBURANE (sodium phenylbutyrate) is used as adjunctive therapy for urea cycle disorders. Monitor plasma ammonia, arginine, and glutamine levels. Avoid in patients with severe hepatic impairment. Discontinue if hyperammonemic encephalopathy occurs. |
| Patient Advice | Take with food or milk to reduce gastrointestinal irritation. · Do not crush or chew tablets; swallow whole. · Report any signs of hyperammonemia (e.g., lethargy, vomiting, confusion) immediately. · Maintain a low-protein diet as prescribed. · Store at room temperature away from moisture and heat. |
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