What is the treatment for a 7g paracetamol (acetaminophen) overdose?

Treatment of 7g Paracetamol Overdose

For a 7g paracetamol overdose, immediately administer N-acetylcysteine (NAC) using the FDA-approved intravenous regimen: 150 mg/kg loading dose over 15 minutes, followed by 50 mg/kg over 4 hours, then 100 mg/kg over 16 hours (total 300 mg/kg over 21 hours). 1

Immediate Assessment and Risk Stratification

• Obtain a serum paracetamol concentration at least 4 hours post-ingestion to plot on the Rumack-Matthew nomogram for risk stratification 2, 1
• If the patient presents within 4 hours of ingestion, administer activated charcoal (1 g/kg orally) just prior to starting NAC to reduce absorption 2, 3
• Do not delay NAC administration while awaiting acetaminophen levels if there is strong suspicion of significant overdose - a 7g ingestion in most adults warrants immediate treatment 3

NAC Treatment Protocol

Standard Dosing Regimen (FDA-Approved)

• Loading dose: 150 mg/kg IV over 15 minutes 1
• Second dose: 50 mg/kg IV over 4 hours 1
• Third dose: 100 mg/kg IV over 16 hours 1
• Total treatment duration is 21 hours with a cumulative dose of 300 mg/kg 1

Critical Timing Considerations

• NAC initiated within 8 hours of ingestion carries only a 2.9% risk of severe hepatotoxicity 2
• Initiation within 10 hours increases risk to 6.1%, while after 10 hours the risk jumps to 26.4% 2
• Even when started after 8 hours, NAC still provides significant benefit and should never be withheld 3

Special Considerations for 7g Ingestion

• A 7g ingestion represents a potentially hepatotoxic dose (exceeding the 4g/day threshold) and warrants treatment regardless of nomogram placement in most clinical scenarios 4, 2
• For patients weighing less than 70 kg, a 7g ingestion represents >100 mg/kg, placing them at higher risk 4
• Patients with risk factors (chronic alcohol use, fasting, enzyme-inducing medications) may develop toxicity at lower doses and should receive NAC even if levels fall below typical treatment thresholds 3

Monitoring During Treatment

• Monitor for hypersensitivity reactions during NAC infusion, particularly during the loading dose when concentrations are highest 1
• Common adverse reactions include rash, urticaria, facial flushing, and pruritus (>2% incidence) 1
• If serious hypersensitivity occurs, immediately discontinue the infusion, treat the reaction, then carefully restart NAC at a slower rate 1
• Obtain liver function tests (AST, ALT) and prothrombin time to assess for developing hepatotoxicity 4

When to Extend Treatment Beyond 21 Hours

• Continue NAC if acetaminophen levels remain detectable after the standard 21-hour protocol 2
• Extend treatment if aminotransferases are rising or remain elevated (AST or ALT >50 IU/L) 2
• For patients with established hepatotoxicity or hepatic failure, continue NAC until clinical improvement occurs 2, 3

Common Pitfalls to Avoid

• Never delay NAC administration to give activated charcoal - charcoal can be given just before NAC, but NAC takes priority 3
• Do not withhold NAC based on a "low" 4-hour level if the history suggests 7g ingestion - inaccurate timing or delayed absorption can lead to false reassurance 2
• Patients may develop hepatotoxicity despite being stratified as "no risk" on the nomogram due to inaccurate history or individual susceptibility 2
• For patients with unknown time of ingestion and a 7g reported dose, start NAC immediately and obtain levels to guide continuation 3, 1

Alternative Considerations

• The newer two-bag acetylcysteine regimen (200 mg/kg over 4 hours, then 100 mg/kg over 16 hours) shows similar efficacy with significantly reduced adverse reactions, though the FDA-approved three-bag regimen remains standard in the United States 5
• Oral NAC (140 mg/kg loading dose, then 70 mg/kg every 4 hours for 17 doses) is an alternative when IV access is problematic, though IV remains preferred 3