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Poisoning Information for the Public & Health Care Professionals
Last updated: 02/2021

Acetylcysteine - Traditional

Parvolex, Mucomyst, N-Acetylcysteine, NAC

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Acetylcysteine - Traditional

Parvolex, Mucomyst, N-Acetylcysteine, NAC

ALERT: NS / PEI / NB hospitals: Please use "Acetylcysteine - Single Concentration". Do NOT use traditional protocol.


  • 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.


a) Intravenous 21-hour protocol

(NAC) 200 mg/mL

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 †


Criteria for Discontinuing NAC:  At the end of the 21 hr protocol, NAC may be discontinued if the following criteria are met:  Negative acetaminophen level, INR less than or equal to 1.5, AST or ALT less than 50 IU/L OR, if elevated, declining and approximately 50% of the peak value measured.  If any of these criteria are not met, continue the NAC at the same concentration and rate as the 3rd infusion. Bloodwork should be done every 4 to 12 hours (depending on the clinical scenario).  As soon as criteria for stopping NAC is reached, NAC can be discontinued. 

* 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 Atlantic Canada Poison Centre for details.


  • 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.


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


  • 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: can be treated with regular anti-nauseant medications if necessary.  
  • 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 an antihistamine 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.


  • 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