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New study aims to reduce antibiotic use for people with a common skin infection

Published: 29 August 2023
Lower leg cellulitis
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A new study, led by researchers in Southampton, is testing whether the amount of antibiotics prescribed to people with a common skin infection could be reduced.

Cellulitis is a deep skin infection which can be potentially serious if left untreated.

But with levels of antibiotic resistance rising, and side effects caused by prolonged antibiotic use, doctors are looking at ways to cut the amount of the drugs being prescribed.

The COAT study, led by Professor Nick Francis from the University of Southampton’s Primary Care Research Centre, will look at whether a shorter course of antibiotics can still be effective at treating cellulitis.

The study is funded by the National Institute for Health and Care Research (NIHR) and is being run by the Southampton Clinical Trials Unit.


Reducing antibiotic use

Cellulitis is a bacterial infection that affects the deep layers of the skin. It is particularly common in older people and those with poor circulation or a weakened immune system, and often affects the legs. If not treated quickly, the infection can spread to other parts of the body and become serious, sometimes requiring hospital treatment.

Current guidelines suggest that people with cellulitis should be given a five to seven-day course of oral antibiotics.


Professor Nick Francis
Professor Nick Francis

“At the moment, almost all patients who come to their GP with cellulitis will be initially treated for the full seven days,” says Nick Francis, Clinical Professor of Primary Care Research at the University of Southampton. “This is not because of evidence from research, but more due to years of warnings to doctors about stopping treatment too soon. However, there is increasing evidence that shorter courses are as effective and that longer courses may increase risks for individual patients, as well as the entire healthcare system as we see increases in antibiotic resistance.”

Several clinical studies have already shown that shorter courses of antibiotics can be just as effective in infections such as pneumonia, tonsillitis, and urinary infections. But there is currently very little evidence for this approach for people with cellulitis.

“This lack of evidence means GPs are reluctant to prescribe shorter courses for these patients,” continues Professor Francis. “Our study will test whether 5 days of antibiotic treatment works as well as seven days to see if the guidelines can be changed.”


Gathering the evidence

The COAT study will recruit over 350 patients with cellulitis in their legs through GP surgeries across the UK. Half will be given the standard seven-day course of the oral antibiotic flucloxacillin, while the other half will have five days of antibiotics followed by two days taking a placebo, or dummy pill.

“The patients will be randomly assigned to each arm of the trial and will not know whether they are having the full course of antibiotics or the shorter course and placebo,” says Sophie Varkonyi-Clifford, Trial Manager at the Southampton Clinical Trials Unit. “Patients will be asked to report pain and other symptoms related to cellulitis before they start treatment and for a month afterwards, while their local GP surgery will also note any additional treatment or complications for the next year.”

Professor Francis concludes, “We hope the outcomes of this trial will definitively show whether cellulitis can be effectively treated with a five-day course of antibiotics. If the results are positive it could lead to an update in the guidelines and see a reduction in the amount of these drugs being routinely prescribed by GPs across the UK, which would be beneficial for patients and the entire health service.”


For more information on the study, the eligibility criteria to take part, and to download the Participant Information Sheet, visit the COAT study website.


Notes for editors

The COAT Study - A blinded, non-inferiority phase III trial of 5 versus 7 days of oral flucloxacillin in primary care patients with lower limb cellulitis. Visit the COAT trial portfolio page.

The Southampton Clinical Trials Unit (SCTU) is a National institute for Health and Care Research (NIHR) supported and Cancer Research UK (CRUK) core-funded CTU with expertise in the design, conduct and analysis of interventional, multi-centre clinical trials. The CTU is based within the University of Southampton with offices at the University Hospital Southampton NHS Foundation Trust Southampton General Hospital site. For more information, visit the SCTU website.

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