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The EXTEND trial: EXTENDed antibiotics to improve outcomes in patients with complicated intra-abdominal infection

What is the EXTEND Trial?

What are complicated intra-abdominal infections?

Bacteria live in the intestine to help digest food. If the intestine is damaged, for example by an operation or a disease such as cancer, bacteria can leak into the space surrounding the intestine (called the abdominal cavity) and cause serious infections known as complicated intra-abdominal infections. Over thirty thousand patients per year suffer from this type of infection.

Why is research into complicated intra-abdominal infections needed?

The care of patients with complicated intra-abdominal infections is a big concern for doctors. The damaged area of the intestine may need to be removed and antibiotics are used to kill any bacteria left in the abdominal cavity. However, this treatment does not seem to be working as well as hoped. In up to half of patients the original infection comes back or patients develop another infection. This means that these patients may need a second round of treatment, including antibiotics and/or an operation.

Research from other trials has suggested that longer courses of antibiotics may offer benefits for patients with serious abdominal infections. If longer courses of antibiotics are better at curing and preventing infections, they may be better at keeping patients out of hospital. This may reduce the chance patients will catch antibiotic resistant infections. 

What will the EXTEND trial involve?

To out whether longer antibiotic courses are better for patients with complicated intra-abdominal infections, the EXTEND trial will group patients by chance into one of two treatment groups. One group will take antibiotics as normal, which is decided by their own doctor (often about 7 to 18 days). The other group will take antibiotics for four weeks.

We will monitor patients in both groups over six months to see whether the treatments prevent the return of the original infection and the development of new infections. Patient quality of life will be assessed during this time through the completion of a questionnaire which asks whether patients have any problems with mobility, self-care, their usual activities, pain/discomfort and anxiety/depression.

What impact will this have?

The results of the research will be shared throughout the NHS and charities to help doctors decide if longer courses of antibiotics will benefit patients with complicated intra-abdominal infections. 

Study status

The study is now open to recruitment: please see the information below for patients or research staff. 

EXTEND TRIAL: Map of participating sites

Conflict of Interest

All individuals involved in the management and design of the EXTEND trial (see “Members" tab) are employed by the NHS and/or a university. There are no conflicts of interest to disclose. This study aims to benefit patients.


The EXTEND trial has received approval from the HRA and Leeds West Research
Ethics Committee (IRAS Reference: 302989; REC Reference: 22/YH/0023).

Privacy Notice: How we use your research data

For Patients

Who can take part?

Adults who are in one of the participating hospitals with a severe gut infection will be invited to take part in EXTEND. Those who join the trial will be put into one of two groups. One group will have antibiotics until their doctor thinks they are better (usually 7 to 18 days). The other group will have antibiotics for 4 weeks. 

How does the trial affect a patient's medical treatment?

Other than the duration of treatment, all other aspects will be in line with standard NHS care. The antibiotic that patients are prescribed is the same drug that their doctor would prescribe if they were not part of the trial. No experimental drugs or placebos will be used. If a patient experiences side effects or the antibiotic does not seem to be working, their doctor can prescribe a different antibiotic (as is normal practice). Patients will be discharged from the hospital when their doctor decides they are ready. They may continue taking antibiotics at home until they have completed their course of antibiotics. No additional visits to the hospital will be required as part of taking part in the trial.

What happens during the trial?
Each participant will be involved in the trial for 6 months. The steps from beginning to end are shown in the diagram below:


The patient information sheet which patients receive can be downloaded below.

EXTEND PIS (PDF , 282kb).

What will we learn from the results of the trial?

It is important for the trial to find out whether treating gut infections with a longer or shorter duration of antibiotics is better at:

  1. preventing treatment failure - this information will be collected from patient records of participants who have given consent as anonymised data.
  2. improving quality of life for patients - this information will be collected from participants on a quality of life questionnaire.
  3. reducing NHS costs - this information will be collected from patient records of participants who have given consent as anonymised data (for hospital visits) and participant questionnaires (for GP visits).
  4. reducing costs to the patient while they are recovering from this type of infection - this information will be collected from participants by questionnaire.

How have patients been involved in designing the trial?

The EXTEND trial has a patient advisory group of 8 individuals who have personally experienced serious infections. They are consulted on key aspects of the trials such as

  • Deciding the primary outcome (what the main result should be) based on what is most important to them as patients
  • Ensuring the patient information makes sense and includes everything a patient would need to know about EXTEND
  • Making this website a useful, informative resource for patients
  • Deciding what information to collect in patient questionnaires so they are easy for patients to complete

 If you have any questions about EXTEND, please contact

For Research Staff

EXTEND Trial Overview Video

If you would like to join the EXTEND trial as a research site, please contact

The study is scheduled to start recruiting participants in July 2022. Trial documents will be available here for recruiting sites.

Researchers who want to be involved in the EXTEND trial will be given training on the trial. They will also need to have completed the following:

If you have any questions about EXTEND, please see our list of Frequently Asked Questions below or contact the trial team by email.

EXTEND Eligibility Criteria (PDF , 138kb)

EXTEND FAQs (MS Excel , 105kb) 

The Associate PI Scheme

Mission statement

To promote trainee, nurse or allied health professional engagement in EXTEND in order to improve study delivery and participant experience while training the next generation of principle investigators (PIs) in infection, critical care and surgical research.


To provide a structured and focussed research training programme for trainees, nurses and allied health professionals. 


Any trainee doctor (FY1-St8 or equivalent), nurse or allied health professional who is not currently working in research.

A minimum of 6 months commitment will be required for gaining Associate PI status.

(See NIHR Associate PI page for further eligibility criteria)


For Associate PIs

  • Gain practical research experience, including the challenges and practicalities of delivering a portfolio study
  • Structured training in research delivery
  • Acknowledgment in study outputs and publications

For the EXTEND study

  • Improved participant recruitment and experience
  • Increased support at study sites


Associate PIs will be directly supervised and mentored by the Local PI with additional support from the EXTEND associate PI ambassadors and CTU. 

  • Associate PI ambassadors: Shadia Ahmed (microbiology/infection), Olivia O’Connor (Surgery), TBC (Critical Care)
  • CTU contact: Catherine Knowlson (Trial co-ordinator)


  • Dissemination to local department.
  • Engagement with staff, research team meetings
  • Maintaining trial documents
  • Screening, recruitment/consent of patients
  • Local staff training
  • Deputising for PI

Mandatory training to be completed

Complicated Intra-Abdominal Infection (cIAI): Study Day/EXTEND Trial Investigators Meeting 15th March 2023

(Video links to most talks can be found below)

09.50 to 10.00: Introduction

Welcome, introduction and defining cIAI

10:00 to 11:10: Specialty management of cIAI

The patient’s perspective: Living with antibiotic resistant abdominal infection (Video not available)

An illustrated guide to antibiotic choice in cIAI (Andrew Kirby

Surgical techniques in the management of cIAI (Dermot Burke) (Not available online)

Reading abdominal CT scans for cIAI (Dr Rachel Hyland: Leeds Teaching Hospitals NHS Trust)

Critical care for patients with cIAI (Tamas Szakmany: Honorary Professor in Intensive Care, Cardiff University)

11:20 to 12:15 Evidence in the prevention and management of cIAI

Preoperative oral antibiotic bowel preparation (Miss Bhamini Vadhwana: General Surgery Registrar, East Suffolk and North Essex NHS Trust)

Fluorescence angiography to prevent anastomotic leak (Dr Alexios Dosis: Research Fellow, The University of Leeds)

Antibiotic durations for sepsis: Guidance and evidence gaps (Paul Dark: Professor of Critical Care Medicine and NIHR CRN National Deputy Medical Director)

Antibiotics for appendicitis (Marja Boermeester: Professor of Surgery, Amsterdam University Medical Centre, Netherlands)

12:45-13:15 Antibiotic duration for cIAI

Views from the DURAPOP trial (Phillipe Montravers: Professor of Anaesthesiology and Critical Care Medicine, Bichat-Claude Bernard University Hospital, Paris, France)

Views from the STOP-IT trial (Robert Sawyer: Professor of Surgery, Western Michigan University Homer Stryker School of Medicine, USA) (Video unavailable)

Views from the CABI trial (Andrew Kirby and Dermot Burke)

13:15 to 15:00: EXTEND trial interactive session

Trial introduction and progress, participant identification, data collection, problem solving and sharing of good practice (York Trials Unit) (Video unavailable)

API Scheme (Ms Olivia Spence, Surgical trainee, Chesterfield Royal Hospital) (Video unavailable)

15:00 to 1600: What’s new and coming in cIAI and panel discussion

Biomarker guided antibiotics in cIAI (Robert Sawyer: Professor of Surgery, Western Michigan University Homer Stryker School of Medicine, USA) (Video unavailable)

DirectAbdo trial: Detecting antibiotic resistance to guide treatment (Phillipe Montravers: Anaesthesiology and Critical Care Medicine, Bichat-Claude Bernard University Hospital, Paris, France)

Rapid antibiotic stewardship: Update on late phase trials (Paul Dark: Professor of Critical Care Medicine and NIHR CRN National Deputy Medical Director)

Complicated Intra-Abdominal Infection (cIAI) Study Day, 15th March 2023

Please see the flyer and programme below for further information.

EXTEND cIAI Study Day (PDF , 6,601kb)

EXTEND Study Day Programme (MS Word , 655kb)

EXTEND Trial Background and Key Information video

EXTEND Trial: Standard care and Interventional care video

For information on the EXTEND trial please contact:



NIHR Health Technology

Assessment (ref 131784)

Start Date: December 2021
End Date: May 2026


YTU Team

External Team

  • Dr Andrew Kirby - Associate Professor and consultant microbiologist, University of Leeds / Leeds Teaching Hospital
  • Mr Dermot Burke - Associate Professor and consultant colorectal surgeon, University of Leeds / Leeds Teaching Hospital
  • Prof Tamas Szakmany - Senior Lecturer and consultant in intensive care, Cardiff University / Aneurin Bevan University Health Board
  • Prof Thomas Pinkney - Senior Lecturer and Honorary Consultant General and Colorectal Surgeon, University of Birmingham / University Hospitals Birmingham
  • Dr Shadia Ahmed - Clinical Research Fellow, Leeds Teaching Hospital
  • Dr Olivia O'Connor - Surgical trainee
  • Dr Armando Vargas-Palacios - Senior research fellow (health economics), University of Leeds

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