Skip to main navigationSkip to main content
The University of Southampton
Southampton Clinical Trials Unit



A blinded, non-inferiority phase III trial of 5 versus 7 days of oral flucloxacillin in primary care patients with lower limb cellulitis.


Cellulitis is a deep infection of the skin and subcutaneous tissues and most often occurs in the legs. It is a painful condition that is associated with inflammation and swelling of the site, and often systemic symptoms such as fever, headache, muscle aches, malaise, and fatigue. Patients report feeling unwell and that it has a significant impact on their mobility and ability to carry out their usual activities.

NICE guidelines recommend oral flucloxacillin 500–1000 mg four times daily for 5-7 days as first-line treatment for most patients with cellulitis in the community, but most prescriptions are dispensed for a 7-day course.

Participants will be randomly allocated to one of two groups. In addition to usual care, participants will either be assigned to a 5-day oral flucloxacillin course or a standard 7-day flucloxacillin course. Participants will be prescribed a 5-day course of oral flucloxacillin, and two additional tablets will be posted to the participants which will either be the antibiotic or a placebo. Participants will be asked to fill out daily questionnaires and express their experiences with the shortened course and taking part in the trial.



  • Assess the effectiveness and safety of 5 days vs standard 7 days of oral flucloxacillin for lower leg cellulitis


  • Evaluate the cost-consequences of a shorter course from an NHS and personal perspective.

Trial Design

COAT is a randomised, 2-arm, blinded, multi-centre, phase III non-inferiority trial with a 6-month internal pilot.

Following consent participants will be randomised 1:1 into 2 arms:

  • Intervention: Flucloxacillin 500mg four times a day (QDS) for 5 days (unblinded NHS prescription) followed by blinded placebo QDS for 2 days (5 days of antibiotic)
  • Control: Flucloxacillin 500mg QDS for 5 days (unblinded NHS prescription) followed by flucloxacillin 500mg QDS (blinded) for 2 days (7 days of antibiotic)

Participants are then followed up for 28 days via daily questionaries for the first 14 days, then a weekly questionnaire at day 21 and 28. At 12 months post randomisation a primary care notes review will be undertaken.

Trial Status

Open to recruitment


Adults from both genders presenting in primary care with unilateral cellulitis of the leg with the following inclusion criteria:

  1. Aged 18 years and over
  2. Currently showing symptoms of cellulitis (such as pain, tenderness, redness, other change in skin colour, warmth to touch) in one leg for 10 days or less
  3. Pain rated as 3/10 or higher on a numerical rating scale (0-10) at baseline assessment
  4. Be willing to be randomised to either trial arm (5-day or 7-day treatment)
  5. Able to complete trial procedures in the English language.



NIHR logo


This trial is funded by the NIHR Health Assessment Program (reference number: NIHR134867)

Senior Trial Manager:

Zina Eminton

Trial Manager:

Sophie Varkonyi-Clifford

Trial Coordinator:

Jemma Turner

Data Manager:

Charlotte Stuart


Contact Information



SAE Reporting


Press releases, video clips and other external websites

(University of Southampton cannot accept responsibility for external websites)


Watch Professor Nick Francis introducing the COAT study.


Privacy Settings