Introduction Paracetamol is the most widely used over the counter analgesic in the world.
Paracetamol overdose is one of the most common reasons for emergency hospital admission. Around 100,000 people present to emergency departments each year in the UK with paracetamol overdose, and around half are admitted for antidote therapy with acetylcysteine.
Most cases in the UK are impulsive acts of self-harm in young people.
Intentional overdose with Paracetamol is increasingly seen amongst young people.
Paracetamol overdose can be associated with hepatic failure and death. Although rare, paracetamol overdose remains the leading cause of acute liver failure in the Western world.
Overdoses from paracetamol alone directly result in an estimated 150 to 200 deaths and 15 to 20 liver transplants each year in England and Wales (data from routinely collected health and coronial statistics).
Pack-size restrictions instituted in the UK in 1998 resulted in modest reductions in large overdoses, liver transplants, and deaths in England and Wales.
Acetylcysteine (NAC) is a highly effective antidote if used within 8 hours of the overdose.
The RCEM position statement November 2021 recommended that the use of the SNAP regime to treat paracetamol toxicity should become the default standard practise in all emergency departments. Prior to this uptake of the SNAP regime had been sporadic across the UK with some early adopter sites utilising in place of the previous 21hr standard 3 bag protocol with the benefit of a reduced length of NAC treatment.
As per the Lancet publication 2019, The SNAP regime has been shown to be as effective as the traditional regime in preventing liver injury, with fewer adverse reactions (anaphylactoid reactions).
RCEM supports the routine use of the SNAP regime.
The SNAP regime not only offers significant benefits to patients in terms of fewer side effects but also reduced length of stay in hospital.
Adult care has transitioned to the SNAP protocol for NAC administration as per TOXBASE, RCEM and NPIS guidance. This has resulted in fewer side effects, increased compliance, and reduced length of stay.
Children and young people currently receive the previous national standard 21hr (3 bag regime).
Implementation of the SNAP regime in children will reduce the risk of confusion related to regime selection when dealing with adults/children in the Emergency Department. Support for the SNAP regime in children has developed nationally since it was developed and implemented in adults. Data (whilst limited) supports its use in children. Use of SNAP has not become empiric practiceacross the Wessex region or UK. Use of SNAP in paediatric care would not preclude further management and care at Kings College Liver Unit.
Implementation of SNAP in children and young people is expected to reduce their length of stay as patients will be medically cleared for CAHMS review sooner. In the same way as evidence has shown a reduced length of stay when used in Adults.
All children and young people require an assessment by CAMHS following an intentional overdose, as per NICE guidance (Self-harm: assessment, management and preventing recurrence) NICE guideline [NG225] Published: 07 September 2022). Please refer to local guidance.
Safeguarding should be considered in all cases
Scope This policy provides guidance on the prescribing and use of N-Acetylcysteine for suspected / confirmed paracetamol toxicity in the Emergency department, Acute Medical Unit(s) and clinical wards, including Childs Health.
This policy applies to staff involved in the management of paracetamol overdose.
Implementation of this policy would ensure that the 12-hour SNAP protocol is used exclusively, in addition:
A prompt assessment of the risk of paracetamol toxicity is done.
The SNAP protocol for NAC is prescribed, initiated, and administered safely.
Administration and treatment is continuous and standardised across wards.
Patients with significant paracetamol hepatotoxicity are managed accordingly and referred to specialists as appropriate.
This policy is aimed at adult patients and children requiring NAC with different prescribing guidelines for weights >40kg or <40kg.
Implementation is in line with NPIS/RCEM guidance November 2021 that the SNAP regime be the UK standard of management.
Purpose The Purpose of this document is to clearly detail the process for the use of N-Acetylcysteine (NAC) in the management of suspected/ confirmed paracetamol toxicity in the Emergency Department (ED), Childrens Assessment Units and Acute Medicines Unit (AMU)
As necessary, list and describe meaning of terms used in policy.
SNAP: The Scottish and Newcastle Anti-emetic Pre-treatment for Paracetamol Poisoning (SNAP) Study demonstrated that a 12 hr NAC regimen was associated with fewer adverse drug reactions compared with the standard 21 h regimen. Further studies showed clinical efficacy.
NPIS: National Poisons Information Service / TOXBASE
RCEM: Royal College of Emergency Medicine
Communication and Training Plans
Guideline to be disseminated via local paediatric and emergency medicine teams with pharmacy support as applicable in EM and paediatric care. TOXBASE/NPIS Guidance highlights “Warning - If paracetamol concentrations are checked during acetylcysteine infusion, some chemical analysers may significantly underestimate paracetamol concentrations by as much as 40% depending on serum acetylcysteine concentrations. NPIS recommends that clinicians ensure results provided by their lab are not affected in this way. If in doubt, check with your lab.” HHFT have confirmed this is not of concern at their local laboratory. As part of role out of this guidance site leads should confirm if this impacts on their respective site
Process for Monitoring Compliance
The purpose of monitoring is to provide assurance that the agreed approach is being followed. This ensures that we get things right for patients, use resources well and protect our reputation. Our monitoring will therefore be proportionate, achievable and deal with specifics that can be assessed or measured.
For a downloadable version of the SNAP Protocol, click here.
Pettie JM, Caparrotta TM, Hunter RW et al. Safety and Efficacy of the SNAP 12-hour Acetylcysteine Regimen for the Treatment of Paracetamol Overdose. EClinicalMedicine. 2019 May 2;11:11-17. doi: 10.1016/j.eclinm.2019.04.005. PMID: 31317129; PMCID: PMC6610779. https://pubmed.ncbi.nlm.nih.gov/31317129/
Toxbase – National Poisons Information Service, 2020. Acetylcisteine – antidote monograph. Available
NICE guideline. Self-harm: assessment, management and preventing recurrence [NG225]. Published: 07 September 2022)
Document Version: 1.0
Lead Authors: Rachel Harrison, PEM Consultant, HHFT Paul Flattery, ED Pharmacist, HHFT
Approving Network: Wessex Paediatric Emergency Medicine Network Date of Approval: