sodium phenylacetate

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sodium phenylacetate/sodium benzoate

(soe-dee-um fen-il-as-e-tate/soe-dee-um ben-zo-ate) ,


(trade name)


Therapeutic: antidotes
Pharmacologic: none assigned


Adjunctive therapy of acute hyperammonemia associated with urea cycle disorders; when lack of specific enzymes results in an inability to breakdown and eliminate waste nitrogens.


Provides an alternative pathway for nitrogen elimination in patients without a fully functioning urea cycle.

Therapeutic effects

Decreased sequelae of hyperammonemia including encephalopathy and death.


Absorption: IV administration results in complete bioavailability.
Distribution: Unknown.
Metabolism and Excretion: Metabolized in the liver as part of the alternative pathway in the urea cycle; also metabolized in the kidney.
Half-life: Unknown.

Time/action profile (blood levels)

IVrapid1–3 hr14–26 hr


Contraindicated in: Hypersensitivity.
Use Cautiously in: Hepatic/renal impairment; Obstetric: Use only if clearly needed; Lactation: Safety not established.

Adverse Reactions/Side Effects

Central nervous system

  • seizures (life-threatening)
  • mental impairment


  • vomiting


  • hyperglycemia

Fluid and Electrolyte

  • hypokalemia


Drug-Drug interaction

Penicillin and probenecid may compete for renal secretion.Valproic acid may contribute to hyperammonemia and negate beneficial effects.


Concurrent IV arginine is required.
Intravenous (Children 0–20 kg) Loading dose over 90–120 min—2.5 mL/kg (provides 250 mg/kg of sodium phenylacetate and 250 mg/kg sodium benzoate) followed by maintenance infusion—2.5 mL/kg (provides 250 mg/kg of sodium phenylacetate and 250 mg/kg sodium benzoate) over 24 hr, continued until oral therapy is initiated.
Intravenous (Children >20 kg) Loading dose over 90–120 min—2.5 mL/kg (provides 250 mg/kg of sodium phenylacetate and 250 mg/kg sodium benzoate) followed by maintenance infusion—55 mL/m2(provides 5.5 g/m2 of sodium phenylacetate and 5.5 g/m2 sodium benzoate) over 24 hr, continued until oral therapy is initiated.


Solution for injection (requires dilution): sodium phenylacetate 10% and sodium benzoate injection 10% in 50–mL vials

Nursing implications

Nursing assessment

  • Assess neurologic status frequently during therapy.
  • Assess infusion site frequently during therapy. Extravasation into peripheral tissues may lead to skin necrosis. If extravasation is suspected, discontinue infusion and resume at a different site. Treatment of extravasation may include aspiration of residual drug from catheter, limb elevation, and intermittent cooling using cold packs.
  • Lab Test Considerations: Monitor plasma ammonia levels frequently during therapy.
    • Monitor CBC and serum electrolytes frequently during therapy; maintain normal levels. May cause hyperglycemia, hypocalcemia, hypokalemia, and anemia.
    • Monitor blood chemistry, pH, and pCO2 frequently during therapy. May cause metabolic acidosis and hyperammonemia.

Potential Nursing Diagnoses

Risk for injury (Indications)


  • Must be diluted and administered through a central line; administration through peripheral lines may cause burns.
    • May cause nausea and vomiting; administer an antiemetic prior to infusion.
    • Do not repeat loading dose; phenylacetate plasma levels are prolonged.
    • Begin infusion as soon as the diagnosis of hyperammonemia is made.
    • Caloric supplementation and restriction of dietary protein are required during therapy. Caloric intake of >80 cal/kg/day should be attempted. Non-protein calories should be supplied as glucose (8–10 mg/kg/min) with Intralipid added.
    • Once elevated ammonia levels have been reduced to normal range, oral therapy, such as sodium phenylbutyrate, dietary management and protein restrictions should be started or reinitiated.
  • Intravenous Administration
  • Intermittent Infusion: Diluent: Dilute with D10W at ≥25 mL/kg before administration. Use a Millex Durapore GV 33 mm Sterile Syringe Filter (0.22 µm ) during the admixture process when injecting Ammonul into the 10% Dextrose IV bag, regardless of whether particulate matter is seen in the vial; particulate matter may not be seen on visual inspection. Solution is stable for 24 hr at room temperature. Do not administer solutions that are discolored or contain particulate matter.
  • Rate: Administer loading dose over 90–120 min.
  • Continuous Infusion: Diluent: Maintenance infusions use same dilution as loading dose and may be continued until elevated plasma ammonia levels have been normalized or patient can tolerate oral nutrition and medications.
  • Rate: Administer maintenance infusion over 24 hr.
  • Additive Compatibility: arginine 10%.
  • Additive Incompatibility: Do not mix or infusion other solutions or medications with sodium phenylacetate and sodium benzoate.

Patient/Family Teaching

  • Explain purpose of medication to parents/caregivers.

Evaluation/Desired Outcomes

  • Decreased sequelae of hyperammonemia including encephalopathy and death.
References in periodicals archive ?
The Phase 2 trial of AMMONUL will provide us with critical insight in systematically evaluating our hypothesis that ammonia plays an important role in the pathogenesis of this multi-factorial disease process.
AMMONUL is indicated as adjunctive therapy for the treatment of acute hyperammonemia and associated encephalopathy in patients with deficiencies in enzymes of the urea cycle.
Sodium phenylacetate and sodium benzoate are marketed for the treatment of urea cycle disorders by Ucyclyd Pharma under the trade name Ammonul.