What are the recommended IV antibiotics for severe cellulitis?

IV Antibiotics for Severe Cellulitis

For severe cellulitis requiring intravenous therapy, vancomycin (30 mg/kg/day in 2 divided doses IV) is the recommended first-line treatment, particularly when MRSA is suspected. 1

First-Line IV Antibiotic Options

For MRSA Coverage (Purulent Cellulitis)

• Vancomycin: 30 mg/kg/day in 2 divided doses IV (adults); 40 mg/kg/day in 4 divided doses IV (children) 1
• Linezolid: 600 mg every 12 hours IV 1
• Daptomycin: 4 mg/kg every 24 hours IV 1, 2
• Ceftaroline: 600 mg twice daily IV 1

For Non-MRSA Coverage (Non-purulent Cellulitis)

• Nafcillin or Oxacillin: 1-2 g every 4-6 hours IV 1
• Cefazolin: 1 g every 8 hours IV 1
• Clindamycin: 600-900 mg every 6-8 hours IV 1

Decision Algorithm for IV Antibiotic Selection

1. Assess severity and type of cellulitis:

   • Purulent (with drainage/exudate): Consider MRSA coverage
   • Non-purulent (no drainage/exudate): Target beta-hemolytic streptococci

2. For severe non-purulent cellulitis:

   • First choice: Cefazolin 1 g every 8 hours IV 1
   • Penicillin-allergic patients: Clindamycin 600-900 mg every 6-8 hours IV 1

3. For severe purulent cellulitis or MRSA risk factors:

   • First choice: Vancomycin 30 mg/kg/day in 2 divided doses IV 1
   • Alternatives: Linezolid, daptomycin, or ceftaroline 1

4. For necrotizing infections or polymicrobial infections:

   • Broad-spectrum coverage: Vancomycin or linezolid plus piperacillin-tazobactam or a carbapenem 1
   • For documented group A streptococcal necrotizing fasciitis: Penicillin plus clindamycin 1

Special Considerations

Outpatient IV Therapy Options

• Once-daily ceftriaxone (1 g IV) has been shown effective for moderate-to-severe cellulitis in outpatient settings 3
• Once-daily cefazolin (2 g IV) plus oral probenecid (1 g) is an effective alternative to ceftriaxone for outpatient treatment 3
  • Note: Patients with chronic venous disease have higher failure rates with this regimen 4
• Twice-daily cefazolin (2 g IV) is another effective outpatient option 5

When to Switch to Oral Therapy

• Consider switching to oral antibiotics after 24-48 hours of IV therapy if:
  • Clinical improvement is observed
  • Fever has resolved
  • Erythema and swelling are improving
  • Patient can tolerate oral medications

Duration of Therapy

• Standard duration: 5-10 days total (IV + oral) 6
• 5 days is as effective as 10 days for uncomplicated cases 6

Important Caveats

• Obtain cultures when possible, especially in severe cases, to guide targeted therapy 6
• Consider surgical consultation for aggressive infections with signs of systemic toxicity or suspected necrotizing fasciitis 1
• Monitor closely for treatment failure, especially in patients with comorbidities like chronic venous disease 4
• Daptomycin has been shown effective in clinical trials for complicated skin and skin structure infections, with similar success rates to vancomycin or semi-synthetic penicillins 2
• In areas with high MRSA prevalence, empiric coverage for MRSA is crucial for treatment success 7

By following this evidence-based approach to IV antibiotic selection for severe cellulitis, you can optimize outcomes while minimizing complications and treatment failures.