Cellulitis treatment
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"cellulitis" AND "treatment" AND "antibiotics"
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Cellulitis Treatment
Overview
Cellulitis is a bacterial infection of the dermis and subcutaneous tissue. The most common causative organisms are beta-hemolytic streptococci (Group A Streptococcus, ~75% of cases) and Staphylococcus aureus (including MRSA). The approach to treatment depends on whether the infection is purulent or non-purulent, and on severity (mild/moderate/severe).
Non-Purulent Cellulitis (Erysipelas and Classic Cellulitis)
Mild to Moderate (Outpatient)
| Drug | Dose |
|---|---|
| Cephalexin | 500 mg PO q6h |
| Dicloxacillin | 500 mg PO q6h |
| Clindamycin | 300-450 mg PO four times daily |
- Duration: 5-7 days (may extend to 10 days based on response)
- Penicillin V (250-1000 mg PO q6h) is the drug of choice for confirmed erysipelas (which is typically pure streptococcal)
- Penicillin allergy: use macrolides or clindamycin
Moderate to Severe (Inpatient IV Therapy)
| Drug | Dose |
|---|---|
| Cefazolin | IV |
| Ceftriaxone | 1 g IV q24h |
| Penicillin G | 1.0-2.0 million units IV q6h |
| Clindamycin | 600-900 mg IV q8h |
Purulent Cellulitis (MRSA Coverage Required)
Mild-Moderate (Outpatient)
| Drug | Dose |
|---|---|
| TMP-SMX (DS) | 1-2 tablets PO twice daily x 7-10 days |
| Doxycycline | 100 mg PO twice daily x 7-10 days |
| Clindamycin | 300-450 mg PO four times daily x 7-10 days |
- Wound culture is recommended when antibiotics are given for purulent infections
- For purulent abscess without systemic infection: incision and drainage alone may suffice in immunocompetent patients; TMP-SMX improves cure rates when added to I&D
Severe (Inpatient IV)
| Drug | Dose |
|---|---|
| Vancomycin | 15-20 mg/kg IV q12h (first-line for MRSA) |
| Linezolid | 600 mg IV/PO q12h |
| Daptomycin | 4 mg/kg IV q24h |
| Telavancin | 10 mg/kg IV q24h |
| Clindamycin | 600 mg IV q8h |
| Ceftaroline | 600 mg IV q12h |
- For sepsis or unclear etiology, add broad coverage: piperacillin-tazobactam 4.5 g IV q6h, or meropenem 500-1000 mg IV q8h
Special Situations
Waterborne Exposure
- Fresh water (Aeromonas hydrophila): ceftazidime 2 g IV q8h or cefepime 2 g IV q8h or ciprofloxacin 750 mg PO q12h + doxycycline 100 mg IV/PO q12h
- Salt water (Vibrio vulnificus): doxycycline 100 mg IV q12h + ceftriaxone 1 g IV q24h
Immunocompromised Patients
Treat as severe disease; hospitalize and use IV antibiotics with broad coverage including MRSA coverage.
If MRSA is suspected (outpatient)
Use clindamycin, doxycycline, or linezolid. TMP-SMX can be combined with a beta-lactam (e.g., cephalexin) to ensure streptococcal coverage alongside MRSA coverage.
Adjunct Measures
- Elevate the affected extremity to reduce swelling
- Immobilize if involving a hand or extremity
- Mark the borders of erythema with a skin marker to monitor progression or regression
- Do NOT use the affected extremity for venipunctures
- Identify and treat any portal of entry (e.g., tinea pedis - use antifungal to prevent recurrence)
- For recurrent cellulitis: prophylactic low-dose penicillin or erythromycin long-term; compression therapy for lymphedema
Indications for Hospitalization
- Systemic signs (fever, tachycardia, hypotension)
- Failure to improve on oral antibiotics within 48-72 hours
- Inability to tolerate oral medications
- Immunocompromised state
- Rapidly spreading infection
- Sepsis
Differential Diagnosis Pitfalls
- Stasis dermatitis: usually bilateral, centered over medial malleoli, no fever, not painful
- Allergic contact dermatitis: itchy, not painful
- Eosinophilic cellulitis: insect bite reaction, less pain, eosinophilia rather than neutrophilia
- Erythema migrans (Lyme): less painful, expanding ring; don't miss this diagnosis
Recent Evidence
A 2024 network meta-analysis (PMID 39240378, Archives of Dermatology Research) compared first- and second-line antibiotics for cellulitis and erysipelas and supports current antibiotic selection strategies. A 2026 systematic review (PMID 41275489) on secondary prevention of cellulitis confirms the benefit of prophylactic antibiotics and compression therapy for reducing recurrence in high-risk patients.
Sources: Tintinalli's Emergency Medicine; Rosen's Emergency Medicine; Andrews' Diseases of the Skin; Washington Manual of Medical Therapeutics; Current Surgical Therapy 14e; Goldman-Cecil Medicine
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