SODIUM PHENYLACETATE AND SODIUM BENZOATE
Clinical safety rating
cautionComprehensive clinical and safety monograph for SODIUM PHENYLACETATE AND SODIUM BENZOATE (SODIUM PHENYLACETATE AND SODIUM BENZOATE).
Sodium phenylacetate and sodium benzoate provide an alternative pathway for nitrogen excretion in patients with urea cycle disorders. Phenylacetate conjugates with glutamine to form phenylacetylglutamine, which is renally excreted, thereby eliminating waste nitrogen. Benzoate conjugates with glycine to form hippurate, which is also excreted in urine, removing ammonia precursors.
| Metabolism | Sodium phenylacetate is metabolized via conjugation with glutamine to form phenylacetylglutamine. Sodium benzoate is metabolized via conjugation with glycine to form hippurate. Both metabolites are rapidly excreted by the kidneys. |
| Excretion | Sodium phenylacetate and sodium benzoate are primarily excreted renally. Phenylacetate is conjugated with glutamine to form phenylacetylglutamine, which is rapidly eliminated in urine. Benzoate is conjugated with glycine to form hippurate, also renally eliminated. Approximately 80-100% of the administered dose is recovered in urine as conjugates and minor metabolites. Fecal excretion is negligible (<5%). |
| Half-life | The terminal elimination half-life of phenylacetate is approximately 0.5-0.8 hours; however, its active conjugate phenylacetylglutamine has a half-life of about 1.2-1.5 hours. For benzoate, the half-life is approximately 0.5-1 hour. In the context of hyperammonemia treatment, the clinical effect correlates with the rapid formation of conjugates, and the half-life reflects quick clearance. In neonates or patients with renal impairment, half-life may be prolonged. |
| Protein binding | Phenylacetate and benzoate are highly protein bound, primarily to albumin. Protein binding is approximately 80-90% for phenylacetate and 75-85% for benzoate. Binding may be saturable at high concentrations. |
| Volume of Distribution | The apparent volume of distribution for both drugs is small, approximately 0.2-0.3 L/kg, indicating limited extravascular distribution. This is consistent with their high protein binding and confinement to the vascular and interstitial spaces. |
| Bioavailability | Oral bioavailability is high, approximately 80-90% for both components, as they are well absorbed. However, for acute hyperammonemia, intravenous administration is preferred to ensure rapid and complete delivery. |
| Onset of Action | Onset of action is rapid when administered intravenously. Serum ammonia levels begin to decline within 1-2 hours of starting IV infusion. Oral administration results in onset within 1-2 hours, but IV is preferred for acute hyperammonemia due to faster effect. |
| Duration of Action | Duration of action for ammonia reduction is typically 4-6 hours after IV administration, requiring continuous infusion or repeated dosing. After oral administration, the effect lasts approximately 4-6 hours. Ammonia levels may rise again if dosing is interrupted, so sustained therapy is necessary until underlying metabolic control is achieved. |
| Molecular Weight | Sodium phenylacetate: 158.09 Da; Sodium benzoate: 144.11 Da |
Intravenous: Loading dose of 5.5 g/m² over 90-120 minutes, then continuous infusion of 5.5 g/m² over 24 hours.
| Dosage form | SOLUTION |
| Renal impairment | Contraindicated if eGFR < 30 mL/min/1.73 m². For eGFR 30-50: reduce dose by 50% and monitor ammonia levels. |
| Liver impairment | No specific adjustment; use with caution in severe hepatic impairment due to potential for increased ammonia. |
| Pediatric use | Same weight-based dosing as adults: 5.5 g/m² IV loading then 5.5 g/m²/24h continuous infusion. |
| Geriatric use | No specific adjustment; monitor renal function and consider reduced dosing based on creatinine clearance. |
| 1st trimester | Limited human data; animal studies show possible fetal harm. Use only if benefit outweighs risk. Avoid if possible. |
| 2nd trimester | May be used for urea cycle disorders if necessary; monitor for maternal and fetal ammonia levels. |
| 3rd trimester | May be used near term; monitor neonate for hyperammonemia and electrolyte disturbances. |
Clinical note
Comprehensive clinical and safety monograph for SODIUM PHENYLACETATE AND SODIUM BENZOATE (SODIUM PHENYLACETATE AND SODIUM BENZOATE).
| Placental transfer | Crosses placenta; degree not well quantified. Animal studies indicate fetal exposure. |
| Breastfeeding | Excreted into breast milk in low amounts; unlikely to cause adverse effects in term infants. Consider risks vs benefits in infants with urea cycle disorders. |
| Lactation Rating | L2 (Safer) |
| Teratogenic Risk | FDA Pregnancy Category C. Animal studies with sodium phenylacetate and sodium benzoate at doses equivalent to human therapeutic exposure have shown teratogenic effects (skeletal and visceral malformations) when administered during organogenesis. Human data are insufficient to determine fetal risk. In the first trimester, potential for teratogenicity exists; use only if maternal benefit outweighs risk. Second and third trimester exposure may be associated with neonatal metabolic alkalosis, hypernatremia, and potential for kernicterus due to displacement of bilirubin from albumin. Avoid use during labor and delivery due to risk of neonatal hyperbilirubinemia. |
| Fetal Monitoring | Maternal: Monitor serum ammonia, electrolytes (especially potassium, bicarbonate), hepatic and renal function tests, and plasma osmolality. Assess for signs of metabolic alkalosis, hypernatremia, or volume overload. Fetal: Ultrasound monitoring for growth and development if exposure occurs during pregnancy. Neonatal: Post-delivery, monitor for hyperbilirubinemia, metabolic acidosis, and neurotoxicity. |
| Fertility Effects | Animal reproductive studies at high doses of sodium phenylacetate and sodium benzoate have shown impaired fertility, including reduced mating behavior and conception rates. Human data are lacking. Potential effects include disturbance of ovarian function and spermatogenesis due to metabolic acidosis or hormonal imbalance. Clinical significance uncertain. |
■ FDA Black Box Warning
WARNING: Contains sodium (approximately 30.2 mg/mL from sodium phenylacetate and sodium benzoate). Use caution in patients with congestive heart failure, severe renal insufficiency, or conditions with sodium retention. Additionally, neurotoxicity has been associated with phenylacetate accumulation; monitor plasma levels.
| Serious Effects |
Hypersensitivity to any componentSevere hepatic failure (risk of toxicity)Uncorrected electrolyte abnormalities (hypernatremia, hypokalemia)
| Precautions | Monitor ammonia levels, electrolytes, and neurological status. Risk of hypernatremia due to sodium content. Phenylacetate may cause neurotoxicity (tremors, agitation, coma) at high concentrations. Use with caution in patients with hepatic or renal impairment. Not recommended for patients with known hypersensitivity to phenylacetate or benzoate. Extravasation risk: avoid extravasation; if occurs, treat locally. |
| Food/Dietary | Administer with food or enteral feeding to reduce gastrointestinal irritation. Avoid high-protein meals during treatment as they may increase ammonia production. No specific food-drug interactions; restrict dietary protein as part of urea cycle disorder management (typically 0.5-2 g/kg/day). |
| Clinical Pearls | Administer intravenously via central line due to hypertonicity (pH 9-9.5). Monitor serum ammonia, potassium, and bicarbonate closely; hypokalemia and metabolic alkalosis are common. Use with caution in renal impairment (dose adjust for GFR <30 mL/min). Discontinue if hypernatremia or volume overload occurs. Caloric content: 2.5 kcal/mL from phenylacetate and benzoate. |
| Patient Advice | This medication is used to remove excess ammonia from your blood due to a urea cycle disorder. · It is given through a central intravenous line; report any pain, redness, or swelling at the infusion site. · You may experience nausea, vomiting, or headache; notify your healthcare provider if severe. · Regular blood tests are necessary to monitor your ammonia levels and electrolytes. · Avoid taking other medications without consulting your doctor, as they may affect ammonia levels. |
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