Edinburgh Clinical Trials


A single-centre, randomised, open label, blinded end-point, safety and efficacy trial of conventional (300 mg/kg) versus higher doses of acetylcysteine (450 mg/kg and 600 mg/kg) in patients with paracetamol overdose (HiSNAP Trial).

Paracetamol overdose is very common. Someone presents to hospital following an overdose every 5 minutes across the UK. This rate is the same as for heart attacks. Despite having an effective antidote called acetylcysteine (NAC), 1 in 10 patients go on to develop liver damage. NAC causes side-effects, such as allergic reactions, that are unpleasant for the patient and may result in this essential treatment being stopped. It is unknown whether increasing the dose of NAC is more effective at preventing liver damage partly because, until recently, dose increases have not been possible due to the side-effects. To address this, we designed a new protocol for giving NAC (the SNAP regimen) that is now used across the UK and has dramatically reduced the risk of patients experiencing side-effects. The improved safety of the SNAP regimen allows us to look at the potential benefits of treating patients with higher NAC doses. This trial will determine whether increasing the NAC dose results in an increase in the breakdown of paracetamol, without causing an unacceptable rate of side-effects. The trial aims to recruit 90 participants who have had a paracetamol overdose from the Emergency Department or Acute Medical Unit (AMU) in NHS Lothian. The trial will compare the effects of NAC given for 12 hours at 1.5 times and double the standard dose with standard treatment (dose groups: standard = 300 mg/kg; 1.5 = 450 mg/kg and double = 600 mg/kg). Paracetamol breakdown will be assessed by measurement of the breakdown products (metabolites) in the blood. Side-effects will be assessed using the symptoms questionnaire we developed for the SNAP Trial. Participants will be followed up for 7 days using their medical notes to review their recovery. The results of this trial are essential information for the next step, a UK-wide trial to determine whether a higher dose of NAC improves the outcome for patients.


Chief Investigator: Prof James Dear

Number and location of participating sites (by region/ country): 1 (2 centres in NHS Lothian)

EudraCT number: n/a

ISRCTN number: tbc


Funder: Chief Scientist Office  

Start and End date

Of grant award: 01 Jan 2023

Of recruitment: Anticipated 01 Feb 2024  

Current Status: In Set Up

Trial Website: n/a

Email: hisnap.trial@ed.ac.uk


UK GDPR Privacy Statement:  If you have participated in the study, you can find out more about how we use your information:

•               at www.hra.nhs.uk/information-about-patients/

•               our leaflet available from www.hra.nhs.uk/patientdataandresearch

•               by asking one of the research team

•               by sending an email to the Data Protection Officer at University of Edinburgh (dpo@ed.ac.uk) or NHS Lothian (Loth.DPO@nhslothian.scot.nhs.uk)

•               by ringing us on 0131 242 3863


Sponsor: Accord, https://www.accord.scot/


Chief Investigator: Professor James Dear

Address: Centre for Cardiovascular Science, Queen’s Medical Research Institute, 47 Little France Crescent, Edinburgh, EH16 4TJ               

Email: james.dear@ed.ac.uk

Trial Manager:

 Kat Oatey  Email: hisnap.trial@ed.ac.uk

Lead Research Nurse:

Ms Anna Miell    Email: Anna.miell@nhslothian.scot.nhs.uk


ECTU involvement: Trial Management, Statistics, Database and Data Management