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Last updated: 07/2015
Antidote
Pediatric

Acetylcysteine

Parvolex, Mucomyst, N-Acetylcysteine, NAC

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Indications

  • Acute acetaminophen overdose (refer to Matthew-Rumack nomogram at end of monograph).
  • Repeated supratherapeutic (chronic) acetaminophen ingestion.
  • Fulminant hepatic failure due to acetaminophen overdose or other hepatotoxic toxins.

Dosage

a) Intravenous 21-hour protocol

Acetylcysteine
(NAC) 200 mg/mL

Dilution
In dextrose 5% in water

Duration of Infusion

First Infusion
150 mg/kg (0.75 mL/kg) of acetylcysteine

Up to maximum dose of 15 grams

Add dose of acetylcysteine to 2.25 mL/kg of IV fluid. Final concentration of 50 mg/mL

1 hour

Second Infusion
50 mg/kg (0.25 mL/kg) of acetylcysteine

Up to maximum dose of 5 grams

Add dose of acetylcysteine to 4.75 mL/kg of IV fluid final concentration of 10 mg/mL

4 hours

Third Infusion 
100 mg/kg (0.5 mL/kg)* of acetylcysteine

Up to maximum dose of 10 grams

Add dose of acetylcysteine to 9.5 mL/kg of IV fluid. Final concentration of 10 mg/mL

16 hours †

 

IMPORTANT NOTES:

* In massive overdoses of acetaminophen resulting in coma, metabolic acidosis, and elevated lactate, higher doses of N-acetylcysteine during the third infusion may be required, particularly during hemodialysis. Contact the Poison Centre for details.

† At completion of either the oral (see below) or intravenous protocol, if there is a positive acetaminophen level, an INR greater than 1.5, or the AST is greater than 50 IU/L, continuation of the maintenance doses is required. Duration will depend on multiple clinical and laboratory parameters and should be discussed with the IWK Regional Poison Centre.

b) ORAL 20 HOUR PROTOCOL

  • Rarely, oral dosing is necessary for patients who develop refractory anaphylactoid reactions to intravenous acetylcysteine.(Refer to Potential Hazards section below)
  • Loading dose: 140 mg/kg = 0.7 mL/kg of a 20% acetylcysteine solution. 
  • Maintenance doses: 70 mg/kg every 4 hours for five doses.

EXAMPLE: ORAL DOSING FOR A 35KG PERSON

Loading dose:

Acetylcysteine 20% 0.7 mL/kg (0.7 mL X 35 kg = 24.5 mL)

Soda/Juice: 2 mL/kg ( 2 mL X 35 kg = 70 mL)

Total Volume to be administered: 24.5 mL of acetylcysteine + 70 mL soda/juice = 189 mL

Administration

  • Intravenous 21-hour protocol: Dilute dose in dextrose 5% in water (most common) or sodium chloride 0.9% and administer according to protocol provided in the “dosage” section.
  • Oral: Calculate and dilute dose according to protocol provided in the “Dosage” section.

Compatibility, Stability

  • Stable for 24 hours diluted in dextrose 5% in water or sodium chloride 0.9% at room temperature.

Potential Hazards of Administration

  • Nausea, vomiting.
  • Monitor heart rate and blood pressure before, during and after infusion.
  • Anaphylactoid reactions (intravenous dosing). Patients should be monitored closely during the first hour of drug administration. Symptoms include: pruritus, rash, facial edema, urticaria, flushing, chest tightness, tachycardia, hypotension and bronchospasm. Anaphylactoid reactions may be related to the rate of administration and often occur during the loading dose. If anaphylactoid symptoms appear, temporarily discontinue the infusion and assess the patient. Administer diphenhydramine if required. If the reaction is severe follow usual practice for treatment of an allergic reaction. Restart the infusion at a slower rate once the patient is stabilized (i.e. reduce the rate of infusion by half). It is not usually necessary to discontinue acetylcysteine. The entire amount of the acetylcysteine must be administered.

Miscellaneous

  • For acute acetaminophen overdose, acetylcysteine is of maximal benefit if initiated within 8 hours post ingestion but is beneficial at greater than 24 hours after ingestion.

Matthew-Rumack Nomogram

Acetaminophen nomogram


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Goldfrank, L. R., Nelson, L. S., Lewin, N. A., Howland, M. A., Hoffman, R. S., (2015). Goldfrank's toxicologic emergencies(Tenth ed.). New York: McGraw Hill.

IWK Regional Poison Centre. (December 2012). Guidelines for pre-hospital and in-hospital acetaminophen (APAP) toxicity repeated supatherapeutic ingestion (RSTI). Unpublished manuscript.

IWK Regional Poison Centre. (April 2013). Guidelines for pre-hospital and in-hospital acetaminophen (APAP) toxicity, single acute ingestion. Unpublished manuscript.

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