At-a-glance
• Typical course length is 5–7 days; reassess at ~48 hours and change if not improving.
• Flucloxacillin is first-line for most adults; choose alternatives for penicillin allergy.
• Admit/urgent review for systemic toxicity, rapidly spreading infection, immunosuppression, or critical sites (e.g., peri-orbital).
Confirm diagnosis and assess severity
- Typical features: unilateral erythema, warmth, swelling, pain/tenderness; erysipelas often has a sharper raised border.
- Consider differentials: DVT, venous eczema/lipodermatosclerosis, contact dermatitis, gout/pseudogout, superficial thrombophlebitis, necrotising soft tissue infection.
- Red flags: severe pain out of proportion, rapidly progressive swelling, skin necrosis/bullae, crepitus, marked systemic toxicity → urgent assessment.
Antibiotics (NICE NG141 – adults)
First-choice oral antibiotic (5–7 days):
- Flucloxacillin 500 mg to 1 g four times daily for 5–7 days.
Alternative oral antibiotics for penicillin allergy (5–7 days):
- Clarithromycin 500 mg twice daily for 5–7 days, or
- Erythromycin (pregnancy) 500 mg four times daily for 5–7 days, or
- Doxycycline 200 mg on day 1, then 100 mg once daily for 5–7 days (avoid in pregnancy; see BNF).
Second-choice oral antibiotic (guided by clinical response, risk factors and local advice):
- Co-amoxiclav 500/125 mg three times daily for 5–7 days (consider if mixed infection suspected, bites, perineal involvement, or treatment failure).
When IV antibiotics are likely: systemically very unwell, unable to take oral, rapidly spreading, immunosuppressed, or critical anatomical sites.
Supportive care and recurrence prevention
- Support: analgesia, limb elevation, mark borders, treat entry points (tinea pedis, eczema, ulcers), consider compression after acute phase if chronic oedema/venous disease (specialist guidance).
- Review at 48 hours: some worsening in first 24–48h can occur, but overall trajectory should improve; if deteriorating, reassess for abscess/necrotising infection or alternative diagnosis.
- Recurrent cellulitis: address predisposing factors (oedema, tinea, skin breaks) and consider referral for prophylaxis decisions per local protocols.
Frequently asked questions
How long should I treat uncomplicated cellulitis?
NICE NG141 lists 5–7 days for most adult oral regimens, with review and extension only if slow clinical response.
When should I suspect necrotising soft tissue infection?
Disproportionate pain, rapid progression, systemic toxicity, skin necrosis/bullae, crepitus, or failure to respond should prompt urgent escalation.
Do I need swabs/blood cultures?
Routine swabs are often low yield unless there is a wound/ulcer or exudate; cultures are more useful if systemically unwell, immunosuppressed, unusual exposures, or treatment failure (follow local policy).
Transparency
This page is an educational, clinician-written summary of publicly available NICE guidance intended for trained healthcare professionals. It uses original wording (not copied text) and should be used alongside the full NICE source, local pathways, and clinical judgement. Doses provided are for general reference; always check the BNF/SPC.