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Date assigned
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Plain English Summary

Background and study aims
Gabapentin is a medicine used to treat epilepsy and nerve pain. Recently, doctors have begun using gabapentin to treat pain after an operation with the intention of reducing the amount of other drugs needed while maintaining good pain relief. Opioid drugs, such as morphine, are the most commonly used drugs to control pain after surgery, but doctors want to try to reduce the amount of opioid drugs because they cause side effects, often delaying discharge from hospital and leading to slower recovery. There is uncertainty about whether adding gabapentin to the usual drug regimen (which includes opioid drugs) will result in good pain relief, fewer side effects overall and faster recovery after surgery. The aim of this study is to find out whether gabapentin reduces the amount of time patients stay in hospital after the operation, the amount of opioid medication they take, and to assess how gabapentin influences pain in hospital and four months after surgery.

Who can participate?
Adults who are undergoing non-emergency heart, lungs or abdominal surgery

What does the study involve?
Participants are randomly allocated into one of two groups. Those in the first group are treated with gabapentin one hour before surgery and for two days after surgery. Those in the second group are treated with an identical looking dummy pill (placebo) at the same timepoints. Pain levels are assessed by asking patients one, four and 12 hours after surgery and then twice a day until they are discharged from hospital. Patients are also followed up until discharge to find out if they have taken opioid pain killers, as well as to assess their quality of life after four weeks and four months.

What are the possible benefits and risks of participating?
There are no guaranteed benefits of participating, however those who receive the gabapentin may have fewer side effects from opioid drugs and may recover from surgery more quickly. The results from this study may help improve management of pain after surgery in the future. Risks of taking part in the study include the risks of side effects from gabapentin. The side effects of gabapentin are usually short lived and will stop when the medication is stopped. These side effects have only been observed in patients who take gabapentin over long periods of time (e.g. to treat epilepsy or long-term pain). Gabapentin is usually well tolerated and it is unlikely that these events will occur in this study where gabapentin is only taken for a short period of time.

Where is the study run from?
1. University Hospitals Bristol NHS Foundation Trust (UK)
2. University Hospitals Southampton NHS Foundation Trust (UK)

When is the study starting and how long is it expected to run for?
June 2017 to June 2021

Who is funding the study?
National Institute for Health Research, Health Technology Assessment Programme (UK)

Who is the main contact?
Professor Chris Rogers

Trial website

Contact information



Primary contact

Prof Chris Rogers


Contact details

Clinical Trials and Evaluation Unit
Bristol Royal Infirmary
Level 7
Marlborough Street
United Kingdom
+44 117 342 2507

Additional identifiers

EudraCT number

2017-002078-38 number

Protocol/serial number


Study information

Scientific title

Effectiveness, cost effectiveness and safety of gabapentin versus placebo as an adjunct to multimodal pain regimens in surgical patients: A placebo controlled randomised controlled trial with blinding (The GAP study)


GAP Study

Study hypothesis

Gabapentin reduces opioid use after surgery and speeds up recovery, thereby reducing post-operative hospital stay compared to standard multimodal analgesia (usual care).

Ethics approval

Not provided at time of registration

Study design

Multi-centre parallel group placebo-controlled pragmatic randomised controlled trial

Primary study design


Secondary study design

Randomised controlled trial

Trial setting


Trial type


Patient information sheet

Not available in web format, please use the contact details below to request a patient information sheet


Pain management after surgery


Participants are randomised in a 1:1 ratio to one of two groups by an authorised member of the local research team using a secure internet-based randomisation system ensuring allocation concealment.

Intervention group: Participants receive gabapentin 600 mg given preoperatively with the patient’s premedication and 600 mg/day (300 mg in the morning and 300 mg in the evening) given postoperatively for two days following extubation (if applicable) within the multimodal analgesic regimens specified by local analgesic protocols.

Control group: Participants receive a placebo which will be taken at the same time points as the active tablet within the multimodal analgesic regimens specified by local analgesic protocols.

Patients in both groups are followed up at approximately four weeks and four months after randomisation for information on pain, adverse events, resource use and quality of life. this information will be collected via postal questionnaires and/or over the phone.

Intervention type



Phase IV

Drug names


Primary outcome measure

Time from start of surgery to hospital discharge is measured by reviewing participant hospital notes at discharge.

Secondary outcome measures

1. Opioid consumption in the period from surgery until hospital discharge is measured by reviewing participant hospital notes at hospital discharge
2. Acute post-operative pain is assessed using the visual analogue scale (VAS) completed at 1, 4 and 12 hours post-surgery and then twice daily to discharge
3. Adverse health events from randomisation to 4 months including side effects of medication (e.g. nausea; vomiting; pruritus; sedation; confusion) and on-going pain are assessed by reviewing participant hospital notes throughout their hospital stay and at discharge, as well as phone calls with the participants at 4 weeks and 4 months after randomisation
4. HRQoL measured using the EQ-5D 5 level questionnaire and Short-form (SF) 12 completed at baseline and at follow-up at approximately 4 weeks and 4 months after randomisation
5. Resource use to 4 months is measured by reviewing participant hospital notes and completion of Resource Use Questionnaires during the hospital stay, at 4 weeks and 4 months
6. Chronic pain is measured using the brief pain inventory (BPI) at baseline and at 4 months after randomisation

Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

1. Over 18 years of age
2. Undergoing non-emergency surgery:
2.1. Cardiac (surgery on the heart and great vessels carried out via midline sternotomy)
2.2. Thoracic surgery (surgery on the lungs and surrounding tissues)
2.3. Abdominal (open or laparoscopic surgery within the abdominal cavity)

Participant type


Age group




Target number of participants


Participant exclusion criteria

1. Expected to have a minimum length of hospital stay of less than 2 days
2. Taking anti-epileptic medication(s)
3. Allergy to gabapentin
4. Planned epidural analgesia
5. Intended use of any gabapentanoids in the peri-operative analgesic protocol other than the study medication (this includes but is not restricted to: pregabalin, enacarbil gabapentin, 4-methylpregabalin and phenibut)
6. Known renal impairment (for such patients, estimated glomerular filtration rate (eGFR) <30ml/min/1.732)
7. Weight <50kg
8. Inability to provide written informed consent to participate in the trial
9. Unwilling to participate in follow-up
10. Prisoners
11. Already taking gabapentin or gabapentanoids
12. Rare hereditary problems of galactose intolerance, the Lapp lactase deficiency or glucose galactose malabsorption
13. Currently taking an investigational medicinal product as part of another clinical trial

Recruitment start date


Recruitment end date



Countries of recruitment

United Kingdom

Trial participating centre

University Hospitals Bristol NHS Foundation Trust
Bristol Royal Infirmary Marlborough Street
United Kingdom

Trial participating centre

University Hospitals Southampton NHS Foundation Trust
Tremona Road
SO16 6YD
United Kingdom

Sponsor information


University Hospitals Bristol NHS Foundation Trust

Sponsor details

Research and Innovation
Level 3
Education Centre
Upper Maudlin Street
United Kingdom

Sponsor type

Hospital/treatment centre



Funder type


Funder name

Health Technology Assessment Programme

Alternative name(s)

NIHR Health Technology Assessment Programme, HTA

Funding Body Type

government organisation

Funding Body Subtype

Federal/National Government


United Kingdom

Results and Publications

Publication and dissemination plan

Planned publication in a high-impact peer reviewed journal.

IPD Sharing statement:
The datasets generated during and/or analysed during the current study are/will be available upon request from the CTEU team on Please also note that anonymised data will be provided on request for ethically approved research. All such requests could be subject to a small charge to cover the costs of preparing the files and associated documentation.

Intention to publish date


Participant level data

Available on request

Basic results (scientific)

Publication list

Publication citations

Additional files

Editorial Notes

06/06/2017: Verified study information with principal investigator.