Acetaminophen Overdose NAC Dosing Calculator

Patient Weight

NAC Protocol

Oral (72-hour)

IV (21-hour)

Important Note

This calculator provides dosing guidance only. Always verify doses and follow your institution's protocols. Consult with a poison control center for complex cases.

About N-acetylcysteine (NAC) for Acetaminophen Overdose

N-acetylcysteine (NAC) is the antidote for acetaminophen (paracetamol) poisoning. It works by replenishing glutathione stores, which are depleted during acetaminophen metabolism, thereby preventing the formation of toxic metabolites that cause liver damage.

NAC is most effective when administered within 8 hours of acetaminophen ingestion, but it can still provide benefit when given later. The decision to administer NAC is typically based on the patient's serum acetaminophen level plotted on the Rumack-Matthew nomogram, along with the time since ingestion and risk factors for hepatotoxicity.

Treatment Protocols

Oral NAC Protocol (72-hour)

The oral NAC protocol consists of a loading dose followed by maintenance doses over 72 hours:

Loading dose: 140 mg/kg
Maintenance dose: 70 mg/kg every 4 hours for 17 additional doses (total of 18 doses)

Oral NAC has a strong, unpleasant sulfur odor and taste, which may cause vomiting. It is often mixed with juice or soda to improve palatability. If vomiting occurs within 1 hour of administration, the dose should be repeated.

Intravenous NAC Protocol (21-hour)

The IV NAC protocol consists of three consecutive infusions over 21 hours:

First infusion: 150 mg/kg over 60 minutes
Second infusion: 50 mg/kg over 4 hours
Third infusion: 100 mg/kg over 16 hours

IV NAC can cause anaphylactoid reactions, particularly during the loading dose. These reactions are generally not true allergic reactions and can often be managed by temporarily stopping the infusion and treating symptoms.

Clinical Considerations

NAC treatment should be initiated based on the Rumack-Matthew nomogram, which plots acetaminophen levels against time since ingestion.
For patients with unknown time of ingestion or delayed presentation (> 24 hours), NAC should be administered if there is any suspicion of significant acetaminophen ingestion.
Patients with risk factors for hepatotoxicity (chronic alcohol use, malnutrition, use of enzyme-inducing drugs) may require NAC at lower acetaminophen levels.
NAC treatment should be continued until acetaminophen levels are undetectable and liver function tests are improving or normal.
Extended NAC treatment may be necessary for patients with evidence of liver injury.

Monitoring During Treatment

Serial acetaminophen levels
Liver function tests (AST, ALT, bilirubin, INR)
Renal function (BUN, creatinine)
Electrolytes
Glucose (NAC can cause hypoglycemia)
Signs of anaphylactoid reactions with IV NAC (rash, bronchospasm, hypotension)

References

Heard KJ. Acetylcysteine for acetaminophen poisoning. N Engl J Med. 2008;359(3):285-292.
Smilkstein MJ, Knapp GL, Kulig KW, Rumack BH. Efficacy of oral N-acetylcysteine in the treatment of acetaminophen overdose. Analysis of the national multicenter study (1976 to 1985). N Engl J Med. 1988;319(24):1557-1562.
Bateman DN, Dear JW, Thanacoody HK, et al. Reduction of adverse effects from intravenous acetylcysteine treatment for paracetamol poisoning: a randomised controlled trial. Lancet. 2014;383(9918):697-704.
Chiew AL, Gluud C, Brok J, Buckley NA. Interventions for paracetamol (acetaminophen) overdose. Cochrane Database Syst Rev. 2018;2(2):CD003328.