What are the appropriate antibiotics for skin and soft tissue infections?

Appropriate Antibiotics for Skin and Soft Tissue Infections

For mild to moderate skin and soft tissue infections, first-line treatment includes cloxacillin, cephalexin, or amoxicillin-clavulanate, while severe infections require vancomycin plus piperacillin-tazobactam or ceftriaxone plus metronidazole, with specific antibiotic selection based on infection type and suspected pathogens. 1

Classification of Skin and Soft Tissue Infections

Skin and soft tissue infections (SSTIs) can be broadly categorized as:

1. Non-necrotizing infections

   • Impetigo
   • Cellulitis
   • Erysipelas
   • Abscesses

2. Necrotizing infections

   • Necrotizing fasciitis
   • Myonecrosis/gas gangrene

Antibiotic Selection Based on Infection Type

Mild to Moderate Non-Necrotizing Infections

First-choice antibiotics:

• Cloxacillin: 500 mg orally four times daily 1
• Cephalexin: 500 mg orally four times daily 1, 2
• Amoxicillin-clavulanate: 875/125 mg orally twice daily 1

For MRSA suspected or confirmed:

• Trimethoprim-sulfamethoxazole: 1-2 double-strength tablets orally twice daily 1
• Doxycycline: 100 mg orally twice daily (not for children <8 years) 1
• Clindamycin: 300-450 mg orally four times daily (caution: increasing resistance) 1

Severe Non-Necrotizing Infections

For hospitalized patients:

• Vancomycin: 15 mg/kg IV every 12 hours (for MRSA coverage) 1
• Cefazolin: 1 g IV every 8 hours (for MSSA) 1
• Clindamycin: 600-900 mg IV every 8 hours 1

Necrotizing Infections

Immediate surgical consultation is mandatory along with broad-spectrum antibiotics:

• Vancomycin (15 mg/kg IV every 12 hours) plus either:

  • Piperacillin-tazobactam (3.375-4.5 g IV every 6-8 hours) 1, 3 or
  • Ceftriaxone (1 g IV every 24 hours) plus metronidazole (500 mg IV every 8 hours) 1

• For documented Group A Streptococcal necrotizing fasciitis:

  • Penicillin (2-4 million units IV every 4-6 hours) plus clindamycin (600-900 mg IV every 8 hours) 1

Special Considerations

Animal and Human Bites

• Amoxicillin-clavulanate: 875/125 mg orally twice daily 1
• Ampicillin-sulbactam: 1.5-3.0 g IV every 6-8 hours (for severe infections) 1

Diabetic Foot Infections

• Mild: Same as mild-moderate non-necrotizing infections
• Moderate to severe: Broad-spectrum coverage as for necrotizing infections 1

Surgical Site Infections

• Trunk or extremity away from axilla/perineum: Cefazolin, cephalexin, or oxacillin/nafcillin 1
• Axilla or perineum: Metronidazole plus either ciprofloxacin, levofloxacin, or ceftriaxone 1

Duration of Therapy

• Uncomplicated infections: 5-7 days 1
• Complicated infections: 7-14 days, based on clinical response 1
• Necrotizing infections: Minimum 14 days, often longer based on clinical response 1

Clinical Pearls and Pitfalls

• Blood cultures are not routinely recommended for uncomplicated SSTIs but should be obtained in patients with systemic symptoms, immunocompromise, or severe infections 1
• Empiric MRSA coverage should be considered in patients with:
  • Prior MRSA infection
  • Nasal colonization with MRSA
  • Injection drug use
  • Systemic inflammatory response syndrome (SIRS)
  • Penetrating trauma 1
• Oral therapy can replace IV therapy once clinical improvement is documented, potentially reducing hospital length of stay 1
• Elevation of the affected area and treatment of predisposing factors (edema, underlying skin disorders) are important adjuncts to antibiotic therapy 1

Antibiotic Selection Algorithm

1. Assess severity (mild, moderate, severe)
2. Consider risk factors for MRSA
3. Evaluate for necrotizing component (requires immediate surgical consultation)
4. Select appropriate antibiotic based on above factors
5. Reassess at 48-72 hours and adjust therapy if needed

Remember that surgical drainage remains the primary treatment for purulent infections, with antibiotics serving as adjunctive therapy in most cases.