What antibiotics should be used if cellulitis is suspected?

Antibiotic Treatment for Suspected Cellulitis

For suspected cellulitis, first-line treatment should be a beta-lactam antibiotic such as cephalexin (500 mg orally four times daily) or dicloxacillin (500 mg orally four times daily) that targets streptococci and staphylococci, with a treatment duration of 5-10 days. 1

Pathogen Considerations and Antibiotic Selection

Non-purulent Cellulitis

• First-line options:

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

• For penicillin allergy:

  • Clindamycin 300-450 mg orally three times daily 1, 3

Purulent Cellulitis or Suspected MRSA

• Consider coverage for MRSA only if:

  • Purulent drainage is present
  • Associated with abscess
  • History of penetrating trauma
  • Previous MRSA infection
  • High local prevalence of MRSA

• MRSA coverage options:

  • Clindamycin 300-450 mg orally three times daily 1, 3
  • Trimethoprim-sulfamethoxazole 1-2 double-strength tablets twice daily 1

Treatment Algorithm

1. Assess severity and type of cellulitis:

   • Non-purulent vs. purulent
   • Mild/moderate vs. severe
   • Presence of systemic symptoms

2. For mild to moderate non-purulent cellulitis:

   • Oral beta-lactam (cephalexin or dicloxacillin) 4, 1
   • Duration: 5 days for uncomplicated cases 4

3. For severe cellulitis or patients unable to tolerate oral medications:

   • Parenteral therapy with:
     • Nafcillin
     • Cefazolin
     • Clindamycin or vancomycin (for penicillin allergy) 4

4. For suspected MRSA involvement:

   • Consider clindamycin or trimethoprim-sulfamethoxazole 1

Important Clinical Considerations

• Streptococci (particularly group A) are the most common cause of typical cellulitis, followed by Staphylococcus aureus 4, 5

• Elevation of the affected area is crucial but often neglected; it promotes drainage of edema and inflammatory substances 4

• Examine and treat underlying conditions that may predispose to infection:

  • Tinea pedis
  • Venous eczema
  • Interdigital toe space maceration
  • Trauma 4, 1

• Most patients with cellulitis can be treated with oral antibiotics from the start 4

Special Circumstances

• Animal bites: Consider Pasteurella coverage (amoxicillin-clavulanate)
• Water exposure: Consider Aeromonas (freshwater) or Vibrio (saltwater) coverage
• Diabetic patients: May require broader coverage and closer monitoring
• Immunocompromised patients: Consider broader coverage and possible hospitalization

Common Pitfalls to Avoid

1. Overuse of broad-spectrum antibiotics for typical non-purulent cellulitis 1, 5

   • Evidence shows that for non-purulent cellulitis, adding trimethoprim-sulfamethoxazole to cephalexin does not improve outcomes 6

2. Unnecessary MRSA coverage for typical cellulitis

   • Despite rising rates of community-acquired MRSA, coverage for non-purulent cellulitis is generally not recommended 5

3. Inadequate duration of therapy

   • 5 days is sufficient for uncomplicated cellulitis 4
   • More severe cases may require 7-10 days 1

4. Failure to elevate the affected area

   • Elevation is crucial for reducing edema and promoting healing 4

5. Overlooking underlying conditions

   • Address predisposing factors to prevent recurrence 4, 1

Remember that cellulitis is a clinical diagnosis based on history and physical examination. If the patient does not improve within 48-72 hours of appropriate antibiotic therapy, consider alternative diagnoses or deeper infection requiring different management.