What oral antibiotics are recommended for a patient with moderate to severe impetigo, considering potential allergies and resistance patterns?

Oral Antibiotics for Impetigo

First-Line Oral Antibiotic Recommendation

For moderate to severe impetigo, cephalexin 25-50 mg/kg/day divided into 4 doses (or 250-500 mg four times daily in adults) for 7 days is the first-line oral antibiotic, with dicloxacillin as an equally effective alternative at the same dosing schedule. 1

Treatment Algorithm Based on Clinical Scenario

For Presumed Methicillin-Susceptible S. aureus (MSSA)

• Cephalexin is the preferred first-line agent at 25-50 mg/kg/day divided into 4 doses for children, or 250-500 mg four times daily for adults, for 7 days 1, 2
• Dicloxacillin is an equally effective alternative at 25-50 mg/kg/day divided into 4 doses for children, or 250 mg four times daily (mild-moderate) to 250 mg every 6 hours (severe) for adults, for 7 days 1, 3
• Co-amoxiclav (amoxicillin-clavulanic acid) is an acceptable alternative that provides coverage for both S. aureus and S. pyogenes, dosed for 7 days 1
• Dicloxacillin should be taken on an empty stomach, at least 1 hour before or 2 hours after meals, with at least 4 fluid ounces of water, and not in the supine position or immediately before bed 3

When MRSA is Suspected or Confirmed

• Clindamycin is the preferred agent at 20-30 mg/kg/day divided into 3 doses for children, or 300-450 mg three times daily for adults, for 7 days 1, 2
• Sulfamethoxazole-trimethoprim (SMX-TMP) is equally effective at 8-12 mg/kg/day (based on trimethoprim component) divided into 2 doses for children, or 1-2 double-strength tablets twice daily for adults, for 7 days 1, 2
• Doxycycline may be used in children over 8 years old at 2-4 mg/kg/day divided into 2 doses for 7 days, but should be avoided in younger children due to permanent dental staining risk 1
• MRSA coverage should be considered empirically in areas with high MRSA prevalence until culture results are available 1

For Penicillin-Allergic Patients

• Clindamycin is the preferred alternative for penicillin-allergic patients at the dosing described above 2
• Avoid cephalosporins (including cephalexin) if the patient has a history of type 1 hypersensitivity reactions (anaphylaxis or hives) to β-lactams 2
• Macrolides such as erythromycin or clarithromycin can be used, though resistance rates to erythromycin are rising and these agents are generally less effective 1, 4

Critical Treatment Considerations

What NOT to Use

• Penicillin alone is seldom effective and should only be used when cultures confirm streptococci alone, as it lacks adequate coverage against S. aureus, which is now the predominant causative organism 1, 2
• Amoxicillin alone should not be used for impetigo because it lacks adequate coverage against S. aureus 1
• Topical clindamycin cream (formulated for acne) should never be used for impetigo, as it lacks FDA indication and has insufficient systemic absorption 2

Duration and Monitoring

• All oral antibiotic regimens require 7 days of treatment, not the shorter 5-day course used for topical agents 1, 2
• If no improvement occurs by 3-5 days of appropriate therapy, reassess for MRSA infection requiring alternative antibiotics, non-compliance, or antibiotic resistance 2
• Obtain cultures from lesions if there is treatment failure, MRSA is suspected, or in cases of recurrent infections 2

When to Choose Oral Over Topical Therapy

• Extensive disease with numerous lesions requires oral antibiotics rather than topical therapy 1, 2
• Lesions on the face, eyelid, or mouth require oral antibiotics 2
• Systemic symptoms (fever, malaise) mandate oral antibiotic therapy 2
• During outbreaks, oral antibiotics are preferred to decrease transmission 1
• Failure of topical therapy after 3-5 days warrants switching to oral antibiotics 2

Special Populations

Pregnant Patients

• Cephalexin is considered a safe alternative for pregnant patients 1, 2

Immunocompromised Patients

• Use a lower threshold for prescribing oral antibiotics 2
• Monitor closely for treatment failure or deeper infection 2
• Consider longer treatment duration based on clinical response 2
• Consider obtaining cultures even for typical-appearing impetigo 2

Elderly Patients

• Be aware of increased risk of torsades de pointes with clarithromycin 5
• Exercise care with intravenous administration due to possibility of thrombophlebitis 3

Common Pitfalls to Avoid

• Do not prescribe oral antibiotics for limited disease when topical mupirocin is appropriate and more effective 1
• Do not use shorter treatment courses than the recommended 7 days for oral antibiotics, as this leads to treatment failure 1
• Do not rely on disinfectant solutions as primary therapy, as there is little evidence they improve impetigo outcomes 1
• Do not forget infection control measures: keep lesions covered with clean, dry bandages, maintain good hand hygiene, and avoid sharing personal items 1, 2