What is the first-line antibiotic choice for an adult patient with infected impetigo?

First-Line Antibiotic Choice for Adult Impetigo

For adults with impetigo, oral cephalexin (500 mg four times daily for 7 days) or dicloxacillin (500 mg four times daily for 7 days) are the first-line antibiotic choices for methicillin-susceptible Staphylococcus aureus (MSSA), while topical mupirocin ointment applied twice daily for 5 days is preferred for limited disease. 1

Treatment Algorithm Based on Disease Extent

Limited Disease (Few Lesions)

• Topical mupirocin 2% ointment applied twice daily for 5 days is the preferred first-line treatment 1
• Topical retapamulin ointment applied twice daily is an alternative 1
• Topical therapy may be superior to oral antibiotics for limited impetigo 2, 3

Extensive Disease (Numerous Lesions)

• Oral antibiotics are recommended when patients have numerous lesions or during outbreaks to decrease transmission 2, 3
• First-line oral options for MSSA:
  • Cephalexin 500 mg four times daily for 7 days 1
  • Dicloxacillin 500 mg four times daily for 7 days 1
• Alternative oral options:
  • Amoxicillin-clavulanate 875/125 mg twice daily for 7 days 1, 2
  • Erythromycin 250 mg four times daily for 7 days (though resistance rates are rising) 1, 4

When to Cover MRSA

If MRSA is suspected (based on local prevalence, previous MRSA infection, or treatment failure), use MRSA-active antibiotics: 1

• Clindamycin 300-450 mg four times daily for 7 days 1
• Trimethoprim-sulfamethoxazole (TMP-SMX) 1-2 double-strength tablets twice daily for 7 days 1
• Doxycycline or minocycline 100 mg twice daily for 7 days 1

Important MRSA Coverage Caveat

• TMP-SMX provides excellent MRSA coverage but inadequate streptococcal coverage 4
• If streptococcal infection is suspected and TMP-SMX is used, consider adding a beta-lactam like amoxicillin 1
• Clindamycin covers both MRSA and streptococci, making it the preferred single-agent option when MRSA is suspected 1, 4

Critical Treatment Considerations

Antibiotics to Avoid

• Penicillin alone is seldom effective for impetigo and should only be used when cultures confirm streptococci alone 2, 3
• Amoxicillin alone lacks adequate coverage against S. aureus, which is now the predominant causative organism 2
• Topical disinfectants are inferior to antibiotics and should not be used 4, 3

Treatment Duration

• Oral antibiotic therapy should be given for 7 days 1, 2
• Topical therapy is given for 5 days 1, 2

Resistance Patterns

• Methicillin-resistant S. aureus (MRSA), macrolide-resistant streptococcus, and mupirocin-resistant streptococcus are all documented 4
• In areas with high MRSA prevalence (>10% resistance), empiric therapy should cover MRSA until culture results are available 1, 2
• Erythromycin resistance rates are rising, limiting its utility 1, 4

When to Obtain Cultures

Cultures are not routinely recommended for typical impetigo 1

Cultures should be obtained in the following situations: 1

• Patients treated with antibiotic therapy who fail to respond
• Patients with severe local infection or signs of systemic illness
• Concern for a cluster or outbreak
• To guide therapy when MRSA is suspected

Prevention of Spread

• Keep draining wounds covered with clean, dry bandages 1, 2
• Maintain good personal hygiene with regular handwashing using soap and water or alcohol-based hand gel 1, 2
• Avoid reusing or sharing personal items (razors, linens, towels) that have contacted infected skin 1, 2

Special Clinical Scenarios

Recurrent Impetigo

• Drain and culture recurrent abscesses early 1
• Consider a 5-day decolonization regimen with intranasal mupirocin twice daily, daily chlorhexidine washes, and daily decontamination of personal items 1

Outbreaks of Poststreptococcal Glomerulonephritis

• Systemic antimicrobials should be used during outbreaks to eliminate nephritogenic strains 2