What antibiotic?

Antibiotic Selection for Skin and Soft Tissue Infections

For skin and soft tissue infections, the first-line antibiotic choice should be based on the type of infection, with dicloxacillin or cephalexin recommended for uncomplicated infections, while doxycycline, clindamycin, or trimethoprim-sulfamethoxazole should be used when MRSA is suspected or confirmed. 1

Antibiotic Selection Algorithm Based on Infection Type

Uncomplicated Skin and Soft Tissue Infections

• First-line options:
  • Dicloxacillin (anti-staphylococcal penicillin)
  • Cephalexin (first-generation cephalosporin) 1

When MRSA is Suspected or Confirmed

• First-line options:
  • Doxycycline 100 mg PO twice daily 1, 2
  • Clindamycin (if susceptible)
  • Trimethoprim-sulfamethoxazole (TMP-SMX) 1

For Specific Pathogens

• Vibrio vulnificus: Doxycycline PLUS Ceftazidime or Ceftriaxone 1
• Aeromonas hydrophila: Doxycycline PLUS Ciprofloxacin or Ceftriaxone 1
• Polymicrobial infections: Vancomycin PLUS Piperacillin/Tazobactam 1

Decision-Making Based on Infection Severity

Mild Infections

• For purulent infections: Incision and drainage may be sufficient without antibiotics 1, 3
• For non-purulent infections: Oral antibiotics as listed above

Moderate Infections (with systemic signs)

• For purulent infections: Incision and drainage plus oral antibiotics
• For non-purulent infections: Oral antibiotics with broader coverage

Severe Infections (failed oral therapy or significant systemic signs)

• For purulent infections: Intravenous antibiotics
• For non-purulent infections: Intravenous antibiotics

Special Considerations

Necrotizing Fasciitis

• First-line therapy: Clindamycin + Piperacillin-tazobactam (with or without vancomycin) 1
• Alternative: Ceftriaxone + Metronidazole (with or without vancomycin) 1

Diabetic Foot Infections

• Mild infections: Dicloxacillin, clindamycin, cephalexin, amoxicillin-clavulanate, or doxycycline 1
• Moderate to severe infections: Levofloxacin, cefoxitin, ceftriaxone, ampicillin-sulbactam, or broader-spectrum agents 1

Important Clinical Pearls

1. Incision and drainage is the primary treatment for purulent skin and soft tissue infections, with antibiotics as adjunctive therapy 1, 3

2. Empiric antibiotic selection should consider local MRSA prevalence. In areas with high MRSA rates, doxycycline, clindamycin, or TMP-SMX should be first-line choices 1

3. Doxycycline is particularly versatile for skin infections as it covers MRSA, streptococci, and many gram-negative organisms including Vibrio and Aeromonas species 2

4. Duration of therapy typically ranges from 5-10 days for uncomplicated infections, and 7-14 days for more severe infections 1

5. Cephalexin remains highly effective for streptococcal and methicillin-susceptible S. aureus infections with cure rates of 90% or higher 4

6. Twice-daily dosing regimens (like doxycycline) may enhance patient compliance compared to four-times-daily regimens 5, 4

7. For surgical site infections, antibiotic selection should be based on the anatomical location and likely pathogens 1

Common Pitfalls to Avoid

1. Overuse of antibiotics for simple abscesses that have been adequately drained. Studies show high cure rates (>90%) with incision and drainage alone for uncomplicated abscesses, even when caused by MRSA 3

2. Failure to consider local resistance patterns when selecting empiric therapy

3. Inadequate surgical debridement before starting antibiotics for complicated infections 6

4. Delayed treatment for severe or necrotizing infections, which can lead to significant morbidity and mortality

5. Not adjusting therapy when culture results become available

By following this evidence-based approach to antibiotic selection for skin and soft tissue infections, you can optimize treatment outcomes while minimizing unnecessary antibiotic use and the development of resistance.