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Cellulitis and Erysipelas

Cellulitis and erysipelas are skin infections, normally caused by a breach in the skin (eg. scratch, insect bite, tinea of the foot). They are treated similarly.

Erysipelas is an infection of dermis and often presents as a well-demarcated, raised, red, tender rash. It is usually caused by Streptococcus pyogenes and occurs more often in the very young and elderly. Cellulitis effects the deeper subcutaneous tissue and is more diffuse in nature. It is most often caused by Streptococci or Staphylococcus aureus.

Skin infections are common presentations to the Emergency Department. Sometimes patients presenting to the ED have already commenced oral antibiotics and are concerned that it has not improved after 24 hours, however this is normal.

Once treatment has commenced, cellulitis will get worse before it gets better. A study by Aboltins et al compared how long extension of cellulitis occurred in patients on oral and IV antibiotics. Cellulitis and redness appeared to grow an average of 1.3 days after commencing oral antibiotics and 1.8 days in the IV group.

It is known that people with cellulitis recover quicker, with fewer side-effects, on oral antibiotics compared to IV antibiotics. First line antibiotics used in cellulitis have excellent oral bioavailability. Amoxicillin has 74-92% oral bioavailability, Flucloxacillin is 79%, Cephalexin is 90-100% and clindamycin 90%.

People on IV antibiotics have more side effects. One dose of IV antibiotics has increased risk of antibiotic-associated diarrhoea. As well as the pain of having a cannula and possible phlebitis caused by administering IV antibiotics.

IV antibiotics are more expensive and patients must have nursing staff administer them. Outside of costs to the health service this also costs the patient time and money having to attend ambulatory care services.

Cellulitis is sometimes misdiagnosed. If a patient is not improving after 36 hours of treatment you need to consider other differential diagnoses such as stasis dermatitis, lipodermatosclerosis, contact dermatitis, dermato-hypersensitivity reaction, lymphedema, gout, erythema migrans or calciphylaxis. Remember cellulitis is rarely bilateral.


Investigations are only indicated if a patient is systemically unwell, or the infection appears severe or you are uncertain of the diagnosis.

Laboratory tests include FBC, CRP, EUC and glucose.

Imaging such as XR or US may be warranted to rule out a foreign body or abscess formation. If necrotising fasciitis is a concern, XR or CT is recommended to look for subcutaneous gas and myonecrosis.


  • Rest and elevate the limb. This is very important to emphasise with the patient. The leg should be above the hip. DO NOT WORK OR STAND.
  • Patients with cellulitis of the upper limb should be provided with a sling.
  • Commence oral antibiotics:
    • Flu-/Dicloxacillin 500 mg, QID for 5 to 10 days, OR
    • Cephalexin 500mg-1 gram, QID for 5 to 10 days, OR
    • For those with penicillin allergy, give Clindamycin 450 mg, TDS for 5 to 10 days.
  • Broader cover may be required in immunocompromised patients.
  • Consider covering for Aeromonas and Vibrio species in patients exposed to water-borne pathogens
    • For those exposed to sea-water, treat as per regular cellulitis and ADD:
      • Doxycycline 100 mg orally, twice daily OR
      • Ciprofloxacin 12.5 mg/kg up to 500 mg orally, twice daily
    • For those exposed to fresh or brackish water there is either one- or two-drug regimes. Treat with:
      • Trimethoprim + sulfamethoxazole 320+1600 mg orally, twice daily for 5-10 days, OR
      • A combination of Flu-/Dicloxacillin 500 mg orally, QID and Ciprofloxacin 500 mg orally, twice daily for 5-10 days.
    • If there is any concern that the water was contaminated with sewerage or soil, ADD on:
      • Metronidazole 400 mg orally, twice daily
  • Ensure patients treat underlying tinea pedis if it is considered to have initiated the cellulitis.
  • Consider IV antibiotics only if a patient is septic and requires immediate peak antibiotic levels. Or in patients who have chronic illness/ co-morbidities that may compromise gut absorption and leave them vulnerable to severe disease.
  • Give the patient the ECI Cellulitis patient factsheet.

Further References and Resources


This is a New Zealand based website written and reviewed by dermatologists to present authoritative facts and resources about the skin for consumers and health professionals.

Relevant Patient Factsheets


  1. Haran JP, Hayward G, Skinner S. Factors influencing the development of antibiotic associated diarrhea in ED patients discharged home: risk of administering IV antibiotics. The American journal of emergency medicine. 2014; 32(10):1195-9. PMID: 25149599
  2. Aboltins, CA et al. Oral versus parenteral antimicrobials for the treatment of cellulitis: a randomized non-inferiority trial. J Antimicrob Chemother. 2015 Feb;70(2):581-6.PMID: 25336165
  3. Jorup-Ronstrom, C et al. The course, costs and complications of oral versus intravenous penicillin therapy of erysipelas. 1984 Nov-Dec;12(6):390-4.PMID: 6394505
  4. Bernard, P et al. Roxithromycin versus penicillin in the treatment of erysipelas in adults: a comparative study. Br J Dermatol. 1992 Aug; 127(2):155-9.PMID: 1390144
  5. Bernard, P et al. Oral pristinamycin versus standard penicillin regimen to treat erysipelas in adults: randomised, non-inferiority, open trial. 2002 Oct 19;325(7369):864. PMID: 12386036
  6. Kilburn, SA et al. Interventions for cellulitis and erysipelas. Cochrane Database Syst Rev. 2010 Jun 16;(6):CD004299. PMID: 20556757

eTG used for antibiotic regimes.

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