Treatment of Skin Infections
For most uncomplicated skin infections, treatment should be guided by infection type and severity: simple impetigo and localized infections respond to topical mupirocin, while cellulitis and erysipelas require oral beta-lactams targeting streptococci, and abscesses primarily need incision and drainage with antibiotics reserved for specific indications. 1
Classification and Initial Assessment
Before initiating treatment, determine infection severity by evaluating for systemic toxicity indicators 1:
- Fever or hypothermia
- Tachycardia (heart rate >100 beats/min)
- Hypotension (systolic BP <90 mm Hg or >20 mm Hg below baseline)
- Pain disproportionate to physical findings, violaceous bullae, cutaneous hemorrhage, skin sloughing, or rapid progression (these suggest necrotizing infection requiring emergent surgical evaluation) 1
Patients with systemic toxicity require hospitalization, blood cultures, complete blood count, creatinine, bicarbonate, creatine phosphokinase, and C-reactive protein levels 1.
Treatment by Infection Type
Impetigo
Topical mupirocin 2% ointment applied three times daily for 4-10 days is first-line treatment for localized impetigo 1. Mupirocin demonstrates superior efficacy compared to bacitracin and neomycin 1.
For patients with numerous lesions or those not responding to topical therapy 1:
- Oral antibiotics effective against both S. aureus and S. pyogenes are required
- Options include: dicloxacillin, cephalexin, amoxicillin-clavulanate, or clindamycin 1, 2
- Treatment duration: 7-10 days 1
Erysipelas
Penicillin (oral or parenteral depending on severity) is the treatment of choice 1. Penicillin V 500 mg four times daily for 7-10 days is appropriate for oral therapy 1.
Cellulitis (Non-purulent)
For diffuse cellulitis without purulent drainage or abscess, empirical therapy targeting beta-hemolytic streptococci is recommended 1:
Outpatient oral options 1:
- Penicillinase-resistant penicillin (dicloxacillin 500 mg four times daily) or
- First-generation cephalosporin (cephalexin 500 mg three times daily)
- Clindamycin 300 mg three times daily (if penicillin-allergic)
If MRSA is suspected or patient fails to respond to beta-lactam therapy within 24-48 hours 1:
- Clindamycin alone (covers both streptococci and MRSA if susceptible) 1
- TMP-SMX 160-800 mg twice daily PLUS a beta-lactam (TMP-SMX alone misses streptococci) 1
- Doxycycline 100 mg twice daily PLUS a beta-lactam 1
- Linezolid 600 mg twice daily (covers both) 1
Treatment duration: 5-10 days, individualized based on clinical response 1.
Purulent Cellulitis and Abscesses
Incision and drainage is the primary and often sufficient treatment for cutaneous abscesses 1, 2. Multiple studies demonstrate 85-90% cure rates with drainage alone 1.
Antibiotics are indicated when 1, 2:
- Systemic signs of infection present
- Patient is immunocompromised
- Multiple lesions or significant surrounding cellulitis
- Abscess involves hand, face, or genitalia
- Failed drainage alone
Empirical antibiotic options for CA-MRSA coverage 1:
- TMP-SMX 160-800 mg twice daily (does not cover streptococci)
- Doxycycline 100 mg twice daily (does not cover streptococci)
- Clindamycin 300 mg three times daily (covers both if susceptible, but 50% of MRSA has inducible resistance) 1
- Linezolid 600 mg twice daily (covers both)
Complicated Skin and Soft Tissue Infections (Hospitalized Patients)
For hospitalized patients with deeper infections, surgical/traumatic wounds, major abscesses, or infected ulcers/burns, empirical MRSA coverage is recommended pending cultures 1:
Intravenous options 1:
- Vancomycin 30 mg/kg/day in 2 divided doses
- Linezolid 600 mg twice daily
- Daptomycin 4 mg/kg once daily
- Telavancin 10 mg/kg once daily
Treatment duration: 7-14 days based on clinical response 1.
Necrotizing Infections
Emergent surgical debridement is paramount—antibiotics are adjunctive 1.
Empirical broad-spectrum therapy must cover gram-positives (including MRSA), gram-negatives, and anaerobes 1, 2:
- Vancomycin PLUS piperacillin-tazobactam 3.37 g every 6-8 hours
- Vancomycin PLUS a carbapenem (imipenem 1 g every 6-8 hours, meropenem 1 g every 8 hours, or ertapenem 1 g daily)
- Vancomycin PLUS cefotaxime 2 g every 6 hours PLUS metronidazole 500 mg every 6 hours
For confirmed streptococcal necrotizing fasciitis: Penicillin 2-4 million units every 4-6 hours PLUS clindamycin 600-900 mg every 8 hours 1, 2. Clindamycin suppresses toxin production 2.
For clostridial myonecrosis (gas gangrene): Clindamycin 600-900 mg every 8 hours PLUS penicillin 2-4 million units every 4-6 hours 1.
Continue antibiotics until no further debridement needed, clinical improvement achieved, and afebrile for 48-72 hours 2.
Animal and Human Bites
All bite wounds require copious irrigation and cautious debridement 1. Primary closure is not recommended except for facial wounds 1.
Amoxicillin-clavulanate 500-875 mg twice daily for 7-10 days is first-line oral therapy 1. This covers Pasteurella multocida (from animal bites), streptococci, staphylococci, and anaerobes 1.
For penicillin-allergic patients 1:
- Doxycycline 100 mg twice daily PLUS metronidazole 250-500 mg four times daily, or
- Moxifloxacin 400 mg daily (covers aerobes and some anaerobes)
Preemptive antibiotics for 3-5 days are recommended for 1:
- Immunocompromised or asplenic patients
- Advanced liver disease
- Moderate to severe injuries, especially to hand or face
- Injuries potentially penetrating periosteum or joint capsule
Critical Pitfalls to Avoid
Do not use TMP-SMX as monotherapy for non-purulent cellulitis—it lacks activity against streptococci, which are the primary cause 1.
Do not rely on clindamycin alone for MRSA without confirming susceptibility—50% of MRSA strains have inducible resistance 1.
Do not use first-generation cephalosporins or dicloxacillin for animal bites—they miss P. multocida 1.
Do not delay surgical consultation when necrotizing infection is suspected—signs like pain disproportionate to findings, violaceous bullae, or rapid progression require immediate surgical evaluation 1.
Reevaluate patients in 24-48 hours if sent home on empirical antibiotics—progression despite treatment may indicate resistant organisms or deeper infection than initially recognized 1.