Treatment of Cellulitis
For typical cases of cellulitis without systemic signs of infection, a 5-day course of antibiotics active against streptococci is recommended as first-line therapy. 1
Classification and Initial Assessment
Severity Assessment
- Mild cellulitis: No systemic signs of infection, localized erythema, warmth, tenderness
- Moderate cellulitis: Systemic signs of infection present
- Severe cellulitis: Associated with SIRS, immunocompromise, or hemodynamic instability
Diagnostic Approach
- Cellulitis is primarily a clinical diagnosis based on expanding erythema, warmth, tenderness, and swelling 2
- Cultures are not routinely recommended for typical cases 1
- Blood cultures should be obtained in patients with:
- Malignancy on chemotherapy
- Neutropenia
- Severe cell-mediated immunodeficiency
- Immersion injuries
- Animal bites
- Systemic inflammatory response syndrome (SIRS)
Antibiotic Treatment Algorithm
First-Line Treatment (Mild Cellulitis)
- Target organism: β-hemolytic streptococci
- Recommended antibiotics:
- Penicillin VK 250-500 mg every 6 hours
- Amoxicillin 500 mg three times daily
- Cephalexin 500 mg every 6 hours
- Dicloxacillin 250 mg every 6 hours 3
- Duration: 5 days 1, 4
Treatment for Moderate Cellulitis
- Target organisms: Streptococci and consider MSSA coverage
- Recommended antibiotics:
- Dicloxacillin 500 mg every 6 hours
- Cefazolin 1 g every 8 hours (IV)
- Clindamycin 300-450 mg every 6-8 hours (for penicillin-allergic patients)
- Duration: 5 days, extend if not improved 1
Treatment for Severe Cellulitis
- Target organisms: Streptococci, MSSA, and consider MRSA in specific situations
- MRSA coverage indicated if:
- Penetrating trauma
- Evidence of MRSA infection elsewhere
- Nasal colonization with MRSA
- Injection drug use
- SIRS present
- Recommended antibiotics for MRSA coverage:
- Vancomycin 15 mg/kg every 12 hours (IV)
- Linezolid 600 mg every 12 hours
- Daptomycin 4 mg/kg daily
- Clindamycin 600 mg every 8 hours (if susceptible)
- For severely compromised patients: Vancomycin plus either piperacillin-tazobactam or imipenem/meropenem 1
Treatment Setting
- Outpatient: For patients without SIRS, altered mental status, or hemodynamic instability
- Inpatient: Consider for:
- Concern for deeper or necrotizing infection
- Poor adherence to therapy
- Severely immunocompromised patients
- Failing outpatient treatment
Adjunctive Measures
- Elevate the affected area 1
- Treat predisposing factors:
- Edema
- Underlying cutaneous disorders
- Examine interdigital toe spaces for fissuring, scaling, or maceration in lower extremity cellulitis 1
- Consider systemic corticosteroids (prednisone 40 mg daily for 7 days) in non-diabetic adults 1
Management of Recurrent Cellulitis
- Identify and treat predisposing conditions:
- Edema
- Obesity
- Eczema
- Venous insufficiency
- Toe web abnormalities 1
- For patients with 3-4 episodes per year despite addressing predisposing factors, consider prophylactic antibiotics:
- Oral penicillin or erythromycin twice daily for 4-52 weeks
- Intramuscular benzathine penicillin every 2-4 weeks 1
- Consider a 5-day decolonization regimen for recurrent S. aureus infections:
- Intranasal mupirocin twice daily
- Daily chlorhexidine washes
- Daily decontamination of personal items (towels, sheets, clothes) 1
Common Pitfalls and Caveats
- Misdiagnosis: Many conditions mimic cellulitis including venous stasis dermatitis, contact dermatitis, and deep vein thrombosis 5
- Overtreatment for MRSA: MRSA coverage is not routinely needed for typical non-purulent cellulitis 5
- Inadequate follow-up: Extend treatment if infection has not improved after 5 days 1
- Failure to address underlying conditions: Treating predisposing factors is crucial to prevent recurrence 1
- Unnecessary cultures: Routine cultures are not recommended for typical cases and have poor yield 1
The evidence strongly supports a 5-day course of antibiotics targeting streptococci for uncomplicated cellulitis, with extension of therapy if the infection has not improved within this time period 1, 4.