N-Acetylcysteine Dosing for a 29 kg Child
For a 29 kg child with acetaminophen overdose, administer N-acetylcysteine (NAC) with a loading dose of 4,060 mg (140 mg/kg) followed by maintenance doses of 2,030 mg (70 mg/kg) every 4 hours for 17 doses. 1, 2
Oral Administration Protocol
The standard oral NAC regimen is clearly defined in the AASLD guidelines and FDA labeling:
- Loading dose: 140 mg/kg = 4,060 mg (4.06 grams)
- Maintenance doses: 70 mg/kg every 4 hours for 17 doses = 2,030 mg (2.03 grams) per dose
Preparation for Oral Administration
NAC must be diluted from the 20% solution to a 5% concentration 2:
- Loading dose preparation: Mix 20.3 mL of 20% NAC solution with 60.9 mL of diluent (diet cola or diet soft drink) = 81.2 mL total of 5% solution
- Maintenance dose preparation: Mix 10.2 mL of 20% NAC solution with 30.6 mL of diluent = 40.8 mL total of 5% solution
Critical point: If the child vomits within 1 hour of any dose, repeat that dose immediately. 2
Intravenous Administration (Alternative Route)
If oral administration is precluded (e.g., active GI bleeding, altered mental status, persistent vomiting), use IV NAC 1:
- Loading dose: 150 mg/kg = 4,350 mg in 5% dextrose over 15 minutes
- Second dose: 50 mg/kg = 1,450 mg over 4 hours
- Third dose: 100 mg/kg = 2,900 mg over 16 hours
Alternative Simplified IV Regimen
Research supports a simplified two-stage IV protocol that may reduce medication errors 3, 4:
- Loading dose: 150 mg/kg = 4,350 mg over 1 hour
- Continuous infusion: 10 mg/kg/hour = 290 mg/hour for 20 hours
This can be prepared as 30 grams NAC in 1 liter of 0.45% saline with 5% dextrose, which is safer than pure 5% dextrose in children to prevent hyponatremia. 3
Timing Considerations
Begin NAC immediately—do not wait for acetaminophen levels if overdose occurred within 24 hours. 1, 2 NAC is most effective when started within 8-10 hours of ingestion, but retains benefit even when started 48+ hours post-ingestion, particularly in preventing progression of established hepatotoxicity. 1, 5
Monitoring and Safety
- Adverse reactions occur in approximately 14% of patients, most commonly transient skin erythema or mild urticaria during the loading dose that rarely requires discontinuation 6
- Anaphylactoid reactions (bronchospasm) are more common with IV administration and can be managed with antihistamines and epinephrine if needed 1
- Monitor liver function tests (AST, ALT, bilirubin, PT/INR) daily if acetaminophen level is potentially toxic 1, 2
Common Pitfall
Do not use activated charcoal after NAC has been started, as it adsorbs NAC and reduces effectiveness. If activated charcoal is indicated for mixed overdose, perform gastric lavage before administering NAC. 2