What antibiotics are used to treat cellulitis of the lower leg?

Antibiotic Treatment for Cellulitis of the Lower Leg

For typical cases of cellulitis of the lower leg, first-line treatment should be an antibiotic active against streptococci, such as penicillin, amoxicillin, dicloxacillin, cephalexin, or clindamycin, with a recommended duration of 5 days if clinical improvement occurs. 1

First-Line Antibiotic Selection

Mild Cellulitis (without systemic signs)

• Oral options:
  • Cephalexin 500 mg four times daily 1, 2
  • Dicloxacillin 500 mg four times daily 1, 3
  • Clindamycin 300-450 mg four times daily (for penicillin-allergic patients) 1, 4
  • Penicillin VK 250-500 mg four times daily 1
  • Amoxicillin or amoxicillin-clavulanate 1

Moderate to Severe Cellulitis (with systemic signs)

• Parenteral options:
  • Cefazolin 1 g every 8 hours IV 1
  • Nafcillin 1-2 g every 4-6 hours IV 1
  • Penicillin G 2-4 million units every 4-6 hours IV 1
  • Clindamycin or vancomycin (for penicillin-allergic patients) 1

Duration of Therapy

• 5 days of antibiotic therapy is as effective as 10 days for uncomplicated cellulitis if clinical improvement occurs within the first 5 days 1, 5
• Treatment should be extended if the infection has not improved within 5 days 1

Special Considerations

When to Consider MRSA Coverage

MRSA is an unusual cause of typical cellulitis, with β-lactam therapy successful in 96% of patients 1. However, consider MRSA coverage when:

• Cellulitis is associated with penetrating trauma 1
• Evidence of MRSA infection elsewhere 1
• Nasal colonization with MRSA 1
• History of injection drug use 1
• Presence of purulent drainage 1
• Presence of systemic inflammatory response syndrome (SIRS) 1

MRSA Coverage Options

• Oral options:

  • Clindamycin alone 1, 4
  • Trimethoprim-sulfamethoxazole (with caution as activity against streptococci is uncertain) 1
  • Doxycycline (with caution as activity against streptococci is uncertain) 1

• Intravenous options:

  • Vancomycin 1
  • Linezolid 1
  • Daptomycin 1
  • Telavancin 1

Adjunctive Measures

• Elevation of the affected area to promote gravity drainage of edema and inflammatory substances 1
• Treatment of predisposing factors such as edema, venous insufficiency, or underlying cutaneous disorders 1
• Careful examination of interdigital toe spaces in lower extremity cellulitis to identify and treat fissuring, scaling, or maceration 1
• Systemic corticosteroids (e.g., prednisone 40 mg daily for 7 days) could be considered in non-diabetic adult patients to hasten resolution 1, 6

Hospitalization Criteria

Consider hospitalization if:

• Concern for deeper or necrotizing infection 1
• Poor adherence to therapy 1
• Infection in a severely immunocompromised patient 1
• Outpatient treatment is failing 1
• Presence of SIRS, altered mental status, or hemodynamic instability 1

Prevention of Recurrence

• Identify and treat predisposing conditions such as edema, obesity, eczema, venous insufficiency, and toe web abnormalities 1
• For patients with 3-4 episodes per year despite addressing predisposing factors, consider prophylactic antibiotics:
  • Oral penicillin or erythromycin twice daily for 4-52 weeks 1
  • Intramuscular benzathine penicillin every 2-4 weeks 1

Common Pitfalls to Avoid

• Overuse of broad-spectrum antibiotics - Streptococci remain the most common cause of cellulitis, and narrow-spectrum agents targeting these organisms are usually sufficient 1, 7
• Unnecessary MRSA coverage for typical cellulitis without risk factors 1, 8
• Prolonged antibiotic courses when 5 days is typically sufficient 1, 5
• Failure to elevate the affected limb, which can delay resolution 1
• Overlooking and not treating predisposing factors, especially in the toe web spaces for lower extremity cellulitis 1