Paracetamol (Acetaminophen) Poisoning Calculator

Acute Ingestion Thresholds

• >150 mg/kg or >10g total: Potentially toxic dose in children
• >200 mg/kg: High risk - urgent assessment required

Rumack-Matthew Nomogram

• Treatment line: 150 mg/L at 4 hours (or 200 mg/L for high-risk patients)
• Valid for: Single acute ingestion, 4-24 hours post-ingestion
• Not valid for: Repeated ingestions, unknown time of ingestion, staggered doses

High-Risk Factors

• Chronic alcohol use
• Malnutrition or eating disorders
• Regular use of enzyme-inducing drugs (e.g., carbamazepine, phenytoin, rifampicin)
• Pre-existing liver disease

NAC Treatment

Most effective when started within 8 hours of ingestion. Should be considered for:

• Any patient with paracetamol level above treatment line
• Ingestion >150 mg/kg when level not yet available (if presenting 8-24h post-ingestion)
• Repeated supratherapeutic ingestions with detectable paracetamol level

Initial Assessment (0-4 hours)

• Calculate dose ingested (mg/kg)
• Consider activated charcoal if <1 hour post-ingestion and >150 mg/kg ingested
• Do NOT check paracetamol level before 4 hours (unreliable)

4-24 Hours Post-Ingestion

• Check paracetamol level at 4 hours (or on presentation if later)
• Plot on Rumack-Matthew nomogram
• Check ALT, AST, INR if level elevated or late presentation
• Start NAC if level above treatment line

>24 Hours Post-Ingestion

• Nomogram not valid - clinical assessment required
• Check paracetamol level, ALT, AST, INR, creatinine
• Consider NAC based on clinical features and hepatotoxicity markers
• Contact toxicology service

Standard IV Regimen (Total: 300 mg/kg over 21h)

Preparation

• NAC supplied as: 20% (200 mg/mL) - dilute to 10% with sterile water, or use 10% (100 mg/mL) if available
• Diluent: 5% dextrose only (NOT saline)
• Do not mix with other medications

Fluid Restriction (<20 kg)

• Minimum volumes: Bag 1 = 25 mL, Bag 2 = 50 mL, Bag 3 = 100 mL
• Target ~7 mL/kg/hour total fluid to avoid overload

Safety

• Anaphylactoid reactions: Common during Bag 1 - rash, bronchospasm
• If reaction: Stop, give antihistamine ± bronchodilator, restart slower
• Monitor closely during first hour

Continue Beyond 21h If:

• INR >1.3, ALT rising/elevated (>50), detectable paracetamol, or hepatotoxicity
• Repeat Bag 3 (100 mg/kg over 16h) until resolved

Monitoring

• Baseline: Paracetamol level, ALT, AST, INR, creatinine
• At 21h: Paracetamol level, ALT, INR
• Discharge: Paracetamol undetectable, ALT falling, INR <1.3