What is the treatment for impetigo on the knee?

Treatment of Impetigo on the Knee

For localized impetigo on the knee, start with topical mupirocin 2% ointment applied three times daily for 5-7 days, and switch to oral antibiotics if the lesion is extensive, not responding after 3-5 days, or if systemic symptoms develop. 1

First-Line Topical Treatment

• Mupirocin 2% ointment applied three times daily for 5-7 days is the first-line treatment for localized impetigo on the knee. 1, 2
• Retapamulin 1% ointment applied twice daily for 5 days is an effective alternative for limited lesions. 1
• Topical mupirocin demonstrates clinical efficacy rates of 71-93% and pathogen eradication rates of 94-100% in clinical trials. 2
• Mupirocin is FDA-approved for impetigo caused by Staphylococcus aureus and Streptococcus pyogenes. 2

When to Switch to Oral Antibiotics

Switch to oral antibiotics if any of the following apply:

• The impetigo is extensive (multiple lesions or large area involved) 1, 3
• No improvement after 3-5 days of topical therapy 1
• Systemic symptoms are present 1
• Topical therapy is impractical 3

Oral Antibiotic Options

For Presumed Methicillin-Susceptible S. aureus (MSSA):

• Dicloxacillin 250 mg four times daily for adults (12 mg/kg/day in 4 divided doses for children) 1, 3
• Cephalexin 250-500 mg four times daily for adults (25 mg/kg/day in 4 divided doses for children) 1, 3
• Amoxicillin-clavulanate 875/125 mg twice daily for adults (25 mg/kg/day of amoxicillin component in 2 divided doses for children) 3

For Suspected or Confirmed MRSA:

• Clindamycin 300-450 mg three times daily for adults (10-20 mg/kg/day in 3 divided doses for children) 1, 3
• Trimethoprim-sulfamethoxazole 1-2 double-strength tablets twice daily for adults (8-12 mg/kg/day based on trimethoprim component in 2 divided doses for children) 1, 3
• Doxycycline 100 mg twice daily (avoid in children under 8 years) 3

Treatment Duration

• Topical antibiotics: 5-7 days 1
• Oral antibiotics: 5-10 days 1, 3

Critical Pitfalls to Avoid

• Penicillin alone is not effective for impetigo as it lacks adequate coverage against S. aureus. 1, 3
• Macrolides (erythromycin) have increasing resistance rates and should be used with caution. 3
• Avoid tetracyclines in children under 8 years of age. 1, 3

When to Obtain Cultures

Obtain cultures from the lesion if:

• Treatment failure occurs 1
• MRSA is suspected 1, 3
• Recurrent infections are present 1

Prevention of Spread

• Keep the lesion covered with clean, dry bandages 1
• Maintain good personal hygiene with regular handwashing 1
• Avoid sharing personal items that contact the skin 1

Special Population Considerations

• Pregnant patients: Cephalexin is generally considered safe; avoid tetracyclines. 1, 3
• Children under 8 years: Avoid doxycycline and other tetracyclines. 1, 3
• Re-evaluate if no improvement after 48-72 hours of oral therapy. 3