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Cellulitis / Erysipelas (Non-Purulent SSTI)

SSTI

Source: IDMP View on spectrum chart →
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Clinical scenario / source

Annotations only — chart still shows the full chemistry of each drug.

1. Clinical Syndrome

Diffuse skin and soft-tissue infection — warmth, erythema, edema, ± lymphangitis — without abscess, fluctuance, or purulent drainage. Erysipelas is the sharply demarcated superficial variant. Both are dominated by β-hemolytic streptococci.

Excludes: purulent SSTI / abscess (use purulent-ssti — different empirics covering S. aureus + MRSA), necrotizing fasciitis (urgent surgical consult — separate syndrome), diabetic foot infection (mixed flora — separate), animal/human bite (separate).

2. Pathogens

Consider the patient: Lymphedema (recurrence), tinea pedis as portal of entry (treat to prevent recurrence), DM (atypical organisms more likely), immunocompromise, IVDU.

Consider the case: Recurrence pattern, response to first-line, signs of systemic toxicity (sepsis criteria) suggesting deeper infection or nec fasc.

Common

Less common

3. Empiric Therapy

TierFirst choiceAlternativesDurationComments
Outpatient
  • 500 mg · PO QID · PO · 5 days (extend to 7–10 d if slow response)
  • 875 mg · PO BID · PO · 5 days
  • 500 mg · PO QID · PO · 10 days

    Pure erysipelas with sharp demarcation.

  • 300–450 mg · PO QID · PO · 5–7 days

    If PCN allergy.

5 days; extend to 7–10 if slow responseMost non-purulent cellulitis is outpatient. Mark erythema border with skin marker and reassess at 48 h.
Admitted to ward
  • 2 g · q8h · IV · 5–7 days
  • 3 g · q6h · IV · 5–7 days
5–7 days; step down to cephalexin / amoxicillin once afebrileSystemic signs, failed outpatient therapy, immunocompromise, or severe illness. IV-to-PO switch as soon as clinically stable.
Admitted to ICU
  • load + AUC-guided · — · IV
  • 4.5 g · q6h · IV
—Source-dependentSevere sepsis or unable to exclude necrotizing fasciitis — surgical consult mandatory. Cellulitis alone rarely needs ICU; if it does, suspect a deeper process.

Add coverage if:

MRSA coverage
  • Penetrating trauma
  • IV drug use
  • Prior MRSA infection / colonization
  • Failed first-line cellulitis therapy
  • Severe sepsis
  • Nasal MRSA colonization

Add:

  • load + AUC-guided · — · IV

    Outpatient: TMP-SMX + cephalexin combo (TMP-SMX has weak strep coverage so pair with β-lactam).

4. Directed Therapy

Cultures rarely positive in non-purulent cellulitis (skip blood + tissue cultures unless atypical / immunocompromised / failure). If purulent drainage develops → reclassify as purulent SSTI and add MRSA coverage.

Recurrent lower-extremity cellulitis: treat tinea pedis, address lymphedema, consider penicillin V suppression 250 mg PO BID for 12 months (PATCH trial showed ~50% reduction).

5. Monitoring

Resolution: erythema demarcation often worsens in the first 24–48 h before improving — pearl, common pitfall. Mark the border with skin marker. Failure to improve by 48–72 h → reconsider DVT, stasis dermatitis, gout, contact dermatitis, or nec fasc (red flags: pain out of proportion, crepitus, bullae, anesthesia, rapid progression).

Toxicity: clindamycin → C. diff risk (pearl: highest among orally available antibiotics); vanco AUC + Cr.

Pearls

Bilateral lower-extremity 'cellulitis' is almost always stasis dermatitis — not infection. Don't reflexively cover MRSA in non-purulent cellulitis (most strep). Mark the erythema border before discharge so the patient can monitor.

References