sodium phenylacetate

sodium phenylacetate/sodium benzoate

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

Ammonul

(trade name)

Classification

Therapeutic: antidotes
Pharmacologic: none assigned

Indications

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.

Action

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.

Pharmacokinetics

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)

ROUTE	ONSET	PEAK	DURATION
IV	rapid	1–3 hr	14–26 hr

Contraindications/Precautions

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

Gastrointestinal

• vomiting

Endocrinologic

• hyperglycemia

Fluid and Electrolyte

• hypokalemia

Interactions

Drug-Drug interaction

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

Route/Dosage

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.

Availability

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)

Implementation

• 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.