Paracetamol Poisoning in children

Paracetamol Poisoning in Children

Paracetamol (acetaminophen) poisoning is a common and potentially fatal emergency in children. UK guidelines, particularly those from the Royal College of Paediatrics and Child Health (RCPCH) and the National Poisons Information Service (NPIS), provide a structured, risk-stratified approach to assessment and management to prevent liver failure.

 

 

Assessment and Risk

A thorough history is the most crucial step. It is a common misconception that a child’s weight is the only factor in determining risk; the timing and formulation of the paracetamol are just as important.

  • Type of Ingestion: Was it a single acute ingestion or staggered over time? Staggered overdoses have a higher risk of liver toxicity.

  • Time of Ingestion: The time of ingestion is critical for plotting on a nomogram. If the time is unknown or unreliable, the child is automatically considered high-risk.

  • Dose: Calculate the dose ingested in mg/kg.

  • Formulation: Liquid paracetamol, often used in children, is absorbed faster than tablets.

 

Risk Stratification

The UK’s NPIS guidelines classify overdoses based on the dose and type of ingestion.

  • Single Acute Ingestion:

    • Low Risk: Ingestions of less than 150 mg/kg (or less than 75 mg/kg if the child has risk factors).

    • High Risk: Ingestions of more than 150 mg/kg (or more than 75 mg/kg if the child has risk factors).

  • Staggered Overdose: Any ingestion over a 24-hour period that exceeds the recommended daily dose is considered a high-risk staggered overdose.

 

Investigations

Blood tests are essential for diagnosis and determining the need for treatment with N-acetylcysteine (NAC).

  • Paracetamol Level: A paracetamol level should be taken at a specific time point after ingestion.

    • For a single acute overdose, a blood sample is typically taken at 4 hours post-ingestion. This level is then plotted on the paracetamol treatment nomogram.

    • If the ingestion time is unknown or staggered, a paracetamol level should be taken immediately.

  • Liver Function Tests (LFTs): ALT and INR (or prothrombin time) should be measured at baseline and then at 24 hours and 48 hours to assess for liver injury.

  • Other: Renal function tests and blood glucose should also be monitored.

 

Management of Paracetamol Poisoning in Children

The management of paracetamol poisoning in children is based on a time-critical protocol to prevent liver damage. The decision to administer the antidote, N-acetylcysteine (NAC), is determined by the time from ingestion, the dose, and the blood paracetamol level.

 

Single Acute Overdose

  • Time from ingestion ≤ 1 hour: Administer activated charcoal within the first hour to reduce absorption, but only if the child is conscious and not at risk of aspiration.

  • Time from ingestion > 4 hours: A blood paracetamol level must be taken. This is then plotted on the paracetamol treatment nomogram to determine if the child is at risk.

    • If the level is on or above the treatment line, start a 20-21 hour intravenous infusion of N-acetylcysteine (NAC).

    • If the level is below the treatment line, no treatment is needed. The child can be discharged after a period of observation with safety netting advice.

  • Time from ingestion is unknown or > 8 hours: The nomogram is not reliable. Start treatment with NAC immediately as the child is considered high-risk.

 

Staggered Overdose

  • Any child with a staggered overdose (ingestion over a 24-hour period that exceeds the recommended dose) is considered high-risk.

  • Action: A paracetamol level should be taken immediately and NAC treatment started without delay. The level will not be plotted on a nomogram but serves as a baseline for monitoring.

 

Monitoring Blood Results and Response

  • Initial Bloods: Liver function tests (ALT, INR), renal function, and blood glucose are measured at baseline.

  • During NAC Infusion: Regular monitoring is crucial.

    • At 24 hours: Repeat LFTs and INR to assess for signs of liver injury. If these are normal and the child is clinically well, NAC may be stopped after the full 20-21 hour course.

    • If LFTs are worsening or the child is showing signs of liver injury (jaundice, confusion, coagulopathy), the NAC infusion should be continued and a discussion with a senior paediatrician and a hepatology or intensive care team is required.

 

Specific Pitfalls and Nuances

  • The 4-Hour Rule: The nomogram is only valid for a single acute overdose with a known time of ingestion. A level taken before 4 hours can be falsely low as absorption may be incomplete.

  • Risk Factors: Risk factors like malnutrition, chronic illness, and drug interactions can lower the toxic threshold. For these children, treatment may be needed even with lower paracetamol levels.

  • False Reassurance: A normal paracetamol level on a single test does not rule out a staggered overdose or a developing toxicity from a delayed-release preparation.

  • Clinical Suspicion: In an unwell child with suspected paracetamol ingestion, treatment with NAC should be started immediately, even before all blood results are available. The risk of waiting is far greater than the risk of giving an unnecessary infusion.

  • Discharge: Before discharge, ensure the child is clinically well, and all relevant blood results (especially the 24-hour LFTs) are reassuring. Provide clear safety netting advice and a referral to mental health services for adolescents.