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Last updated: 07/2015
Antidote
Adult

Acetylcysteine

Parvolex, Mucomyst, N-Acetylcysteine, NAC

Print Monograph

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

  • Loading Dose: 150 mg/kg acetylcysteine IV in 200 mL dextrose 5% in water over 60 minutes immediately followed by:
  • Second Infusion: 50 mg/kg acetylcysteine IV in 500 mL dextrose 5% in water over 4 hours, immediately followed by:
  • Third Infusion: 100 mg/kg acetylcysteine IV in 1000 mL dextrose 5% in water over 16 hours*†.
Body
weight (kg)

Loading dose
(in 200 mL dextrose 5% in water over 60 minutes)

20% Acetylcysteine solution (mL)

2nd Infusion
(in 500 mL dextrose 5% in water over 4 hours)

20% Acetylcysteine solution (mL)

3rd Infusion
(in 1 L dextrose 5% in water over 16 hours)*†

20% Acetylcysteine solution (mL)

40 - 50 38 13 25
51 - 60 45 15 30
61 - 70 53 18 35
71 - 80 60 20 40
81 - 90 68 23 45
91 - 100 75 25 50
Greater than 100 75 25 50

IMPORTANT NOTES:
*
At completion of either the oral (see below) or intravenous protocol, if there is a positive acetaminophen level, or 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. 

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 IWK Poison Centre for details.

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 20% acetylcysteine solution 
  • Maintenance doses: 70 mg/kg every 4 hours for five doses.
EXAMPLE: ORAL DOSING FOR A 70KG PERSON
Loading Dose:
Acetylcysteine 20%: 0.7 mL/kg ( 0.7 mL X 70 kg = 49 mL)
Soda/Juice: 2 mL/kg (2 mL X 70 kg = 140 mL)
Total Volume to be administered: 49 mL of Acetylcysteine + 140 mL Soda/Juice = 189 mL

Administration

  • Intravenous 21 hour protocol: Dilute dose in dextrose 5% in water (most common) or sodium chloride 9% and administer according to protocol provided in the “Dosage” section.
  • Oral: Calculate and dilute dose according to 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 the 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.

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