Cellulitis is a common bacterial skin infection causing significant pain, swelling and impact on daily activities, frequently leading to emergency department presentations and hospital admissions. While antibiotics are the mainstay of treatment, they do not directly address inflammation, often resulting in persisting or worsening symptoms in the initial days. Corticosteroids, with their potent anti-inflammatory effects, have shown benefit in other acute infections but are not currently standard care for patients with cellulitis. This trial aims to determine if adjunctive oral dexamethasone can reduce pain and improve outcomes in adults with cellulitis presenting to UK urgent secondary care settings.

This is a pragmatic, multicentre, double-blind, placebo-controlled, randomised, parallel group, phase 3 superiority trial, with an internal pilot and parallel health economic evaluation. Adult patients (≥16 years) with a clinical diagnosis of cellulitis (at any body site except the orbit) presenting to urgent secondary care will be screened for eligibility. 450 participants will be randomised (1:1) to receive either two 8 mg doses of oral dexamethasone or matched placebo, administered approximately 24 hours apart, in addition to standard antibiotic therapy. The primary outcome is total pain experienced over the first 3 days postrandomisation, calculated using the standardised area under the curve from pain scores (Numerical Rating Scale 0–10) across up to seven timepoints. Secondary outcomes include health-related quality of life (EuroQol 5 Dimension 5 Level), patient global impression of improvement, analgesia and antibiotic usage, hospital (re)admissions, complications, unscheduled healthcare use, cellulitis recurrence and cost-effectiveness at 90 days. The primary estimand will apply a treatment policy approach to intercurrent events.

The trial has received ethical approval from South Central—Oxford B Research Ethics Committee (reference: 24/SC/0289) and will be conducted in compliance with Good Clinical Practice and applicable regulations. Informed consent will be obtained from all participants. A model consent form can be seen in . Findings will be disseminated through peer-reviewed publications and conference presentations, and to patient groups and relevant clinical guideline committees.

ISRCTN76873478.