What is the first-line antibiotic treatment for cellulitis?

First-Line Antibiotic Treatment for Cellulitis

Cephalexin (500mg orally 4 times daily) is the first-line antibiotic treatment for non-purulent cellulitis, targeting the most common causative organisms including β-hemolytic streptococci and methicillin-sensitive Staphylococcus aureus. 1

Antibiotic Selection Algorithm

1. For standard non-purulent cellulitis:

   • First choice: Cephalexin 500mg orally 4 times daily 1
   • Alternative options (if penicillin allergic): Clindamycin 600mg orally three times daily 1

2. When MRSA risk factors are present:

   • Consider adding or switching to an MRSA-active agent:
     • Clindamycin 600mg orally three times daily (covers both streptococci and CA-MRSA) 1
     • Trimethoprim-sulfamethoxazole (TMP-SMX) 1
     • Note: In areas with high MRSA prevalence, TMP-SMX has shown higher success rates (91%) compared to cephalexin (74%) 2

Treatment Duration

• Standard duration: 7-14 days for uncomplicated cellulitis 1
• Short-course option: 5-7 days may be sufficient for uncomplicated cases, as recommended by NICE 1, 3
• Extended duration (3-4 weeks) may be necessary for:
  • Proximity to prosthetic joints
  • Slow-resolving infections 1

Clinical Considerations and Monitoring

• Culture the affected area early in the course of infection to guide antibiotic selection, especially for recurrent infections 1
• Monitor daily for clinical response
• If no improvement after 5 days, consider:
  • Extending treatment duration
  • Changing antibiotics
  • Reevaluating for deeper infection 1

Special Scenarios

High MRSA Prevalence Areas

In communities with high MRSA prevalence, antibiotics with activity against MRSA (clindamycin or TMP-SMX) may be preferred for empiric therapy 2. However, a randomized controlled trial showed that adding TMP-SMX to cephalexin did not improve outcomes for non-purulent cellulitis 4, suggesting that standard therapy remains appropriate in most cases.

Recurrent Cellulitis

• Identify and treat predisposing factors:

  • Tinea pedis
  • Venous eczema
  • Trauma
  • Edema
  • Obesity
  • Venous insufficiency
  • Toe web abnormalities 1

• For patients with 3-4 episodes per year despite treatment of predisposing factors, consider prophylactic antibiotics:

  • Oral penicillin or erythromycin twice daily for 4-52 weeks
  • Intramuscular benzathine penicillin every 2-4 weeks 1

Common Pitfalls to Avoid

1. Overuse of MRSA coverage: While MRSA is increasingly prevalent, standard non-purulent cellulitis is still predominantly caused by streptococci and MSSA. Cost-effectiveness analysis shows cephalexin remains the most cost-effective therapy at current estimated MRSA levels 5.

2. Inadequate treatment duration: While shorter courses (5 days) may be effective for uncomplicated cases 3, ensure complete resolution before stopping therapy.

3. Failure to identify and treat underlying conditions: Addressing predisposing factors is crucial for preventing recurrence 1.

4. Neglecting supportive care: Elevate the affected area during acute episodes to reduce edema and promote drainage of inflammatory substances 1.

By following this evidence-based approach to cellulitis treatment, clinicians can provide effective therapy while practicing appropriate antibiotic stewardship.