Management of Cellulitis (Evidence‑Based Recommendations)

Diagnosis and Classification

Distinguish purulent from non‑purulent cellulitis to determine the antimicrobial target (MRSA vs. β‑hemolytic streptococci) 1.

Empiric therapy: Oral β‑lactam antibiotics (e.g., cephalexin) targeting β‑hemolytic streptococci are recommended for out‑patients 1.
Add MRSA coverage only when:
Duration of therapy: A 5‑day course is sufficient for patients showing clinical improvement; extend only if erythema, warmth, or swelling have not improved by day 5. No evidence supports courses longer than 5 days in responders 1.

Pathogen predominance: Community‑acquired MRSA is the predominant pathogen; routine streptococcal coverage is generally unnecessary 2.
First‑line oral agent: Clindamycin 300–450 mg three times daily for 5 days (covers MRSA and streptococci) 2.
Alternative MRSA‑active oral agents (require additional β‑lactam for streptococcal coverage):
Prescribing pitfalls: Do not use TMP‑SMX or doxycycline as monotherapy when streptococcal infection is possible; combine with a β‑lactam 2.
Avoid rifampin as monotherapy or adjunctive therapy because it offers no benefit and promotes resistance 3, 4.
Contraindications:

Admit and start IV antibiotics if any of the following are present: systemic toxicity (fever, hypotension, altered mental status, SIRS), rapid progression despite appropriate oral therapy, multiple infection sites or deep‑tissue involvement, significant comorbidities (diabetes, immunosuppression, chronic liver/kidney disease), extremes of age, abscess in difficult‑to‑drain locations (face, hand, genitalia), or concern for necrotizing infection 1, 2.

Vancomycin 15–20 mg/kg IV every 8–12 h – first‑line MRSA coverage 2.
Linezolid 600 mg IV or PO twice daily – alternative to vancomycin 2.
Daptomycin 4 mg/kg IV once daily 2.
Combination therapy for suspected polymicrobial or resistant infection: vancomycin plus piperacillin‑tazobactam or a carbapenem 1.

Elevate the affected limb to reduce edema and facilitate drainage 1, 2.
Examine interdigital toe spaces and treat tinea pedis, fissuring, or maceration to prevent recurrence 1.
Address predisposing factors such as venous insufficiency, lymphedema, obesity, and chronic skin conditions 1.

Re‑evaluate at 48–72 h to confirm reduction in erythema, warmth, swelling, and tenderness 2.
Switch to oral therapy once systemic signs resolve and the patient is clinically improving 1.
Do not extend antibiotics beyond 5 days unless clinical improvement has stalled 1.

Obtain cultures early in recurrent episodes and treat with a 5–10 day course directed at the isolated pathogen 1.
Implement a 5‑day decolonization regimen for recurrent S. aureus: intranasal mupirocin twice daily, daily chlorhexidine washes, and decontamination of personal items 1.
Search for local anatomic causes (e.g., pilonidal cyst, hidradenitis suppurativa, retained foreign material) at sites of recurrence 1.

Cellulitis is a clinical diagnosis; routine blood or skin cultures are not required 1.
Obtain blood cultures in patients with malignancy, neutropenia, severe immunodeficiency, or systemic signs of infection 1.

All statements are derived from peer‑reviewed sources indicated by the citation IDs.