What antibiotic should be used to treat a localized infected scab (impetigo)?

Treatment of Infected Scab (Impetigo)

For localized infected scabs (impetigo), topical mupirocin 2% ointment applied three times daily for 5-7 days is the first-line treatment, but switch to oral antibiotics if the infection is extensive, involves the face/mouth, or fails to improve after 3-5 days. 1, 2, 3

Initial Assessment and Treatment Selection

When to Use Topical Therapy

• Topical mupirocin 2% ointment three times daily for 5-7 days is appropriate for limited, localized impetigo 1, 2, 3
• Mupirocin is superior to placebo with cure rates of 71% versus 35%, and achieves 94% pathogen eradication 3
• Fusidic acid is equally effective as mupirocin if available 4
• Do not use topical clindamycin cream—it lacks FDA approval for impetigo and has insufficient systemic absorption 2
• Bacitracin and neomycin are considerably less effective and should not be used 2

When to Switch to Oral Antibiotics

Oral antibiotics are required when: 1, 2

• Lesions are extensive or widespread
• Lesions involve the face, eyelid, or mouth
• No improvement after 3-5 days of topical therapy
• Systemic symptoms are present (fever, malaise)
• Need to limit spread during outbreaks
• Patient cannot comply with three-times-daily topical application

Oral Antibiotic Selection

For Presumed Methicillin-Susceptible S. aureus (MSSA)

First-line options for 7 days: 1, 2

• Cephalexin 250-500 mg four times daily (adults) or 25-50 mg/kg/day divided four times daily (children)
• Dicloxacillin 250 mg four times daily (adults) or 12.5-25 mg/kg/day divided four times daily (children)
• Do not use penicillin alone—it lacks adequate coverage against S. aureus 2

For Suspected or Confirmed MRSA

MRSA-active options for 7-10 days: 1, 2

• Clindamycin 300-450 mg three times daily (adults) or 10-13 mg/kg/dose three times daily (children)
• Trimethoprim-sulfamethoxazole 1-2 double-strength tablets twice daily (adults) or 8-12 mg/kg/day (based on trimethoprim component) divided twice daily (children)
• Doxycycline or minocycline (avoid in children <8 years old) 1

Penicillin-Allergic Patients

• Clindamycin is the preferred alternative 2
• Avoid cephalosporins if type 1 hypersensitivity (anaphylaxis/hives) to β-lactams 2

Special Populations and Considerations

Pediatric Patients

• Avoid tetracyclines (doxycycline, minocycline) in children under 8 years of age 1, 2
• Mupirocin ointment showed 78% cure rates in children aged 2 months to 15 years 3
• For minor infections in children, topical mupirocin is appropriate 1

Pregnant Patients

• Cephalexin is a safe alternative 2

Immunocompromised Patients

• Use a lower threshold for oral antibiotics 2
• Monitor closely for treatment failure or deeper infection 2
• Consider longer treatment duration based on clinical response 2

When to Obtain Cultures

Obtain bacterial cultures when: 1, 2

• Treatment failure after appropriate therapy
• MRSA is suspected or there is concern for resistant organisms
• Recurrent infections
• During outbreaks
• In immunocompromised patients

Infection Control Measures

Critical prevention strategies: 1, 2

• Keep draining wounds covered with clean, dry bandages
• Maintain good hand hygiene with soap and water or alcohol-based gel
• Avoid sharing personal items that contact the skin (towels, razors, clothing)
• Athletes should be excluded from participation until 24 hours after starting antibiotics and lesions are covered 2

Common Pitfalls to Avoid

• Do not use penicillin alone—it is ineffective against S. aureus 2
• Do not use trimethoprim-sulfamethoxazole as monotherapy for initial cellulitis—it lacks adequate streptococcal coverage 1
• Do not use topical disinfectants—they are inferior to antibiotics 1, 4
• Do not use topical clindamycin cream formulated for acne—it is not indicated for impetigo 2

Reassessment if No Improvement

If no improvement by 3-5 days, consider: 2

• MRSA infection requiring alternative antibiotics
• Deeper or more complex infection than initially estimated
• Non-compliance with therapy
• Antibiotic resistance
• Need for bacterial culture to guide therapy

Outbreak Management

During community outbreaks: 2

• Use systemic antimicrobials to eliminate nephritogenic strains of S. pyogenes
• Consider decolonization with topical nasal mupirocin (twice daily for 5-7 days) for S. aureus carriers 1
• Involve public health authorities to coordinate control measures 2