What are the recommended oral antibiotics for treating impetigo?

Oral Antibiotic Treatment for Impetigo

For impetigo requiring oral therapy, use cephalexin (25-50 mg/kg/day divided into 4 doses) or dicloxacillin (25-50 mg/kg/day divided into 4 doses) for 7 days as first-line treatment; switch to clindamycin (20-30 mg/kg/day divided into 3 doses) or sulfamethoxazole-trimethoprim (8-12 mg/kg/day divided into 2 doses) when MRSA is suspected or in areas with high MRSA prevalence. 1, 2

First-Line Oral Antibiotics for Methicillin-Susceptible Infections

The Infectious Diseases Society of America (IDSA) guidelines specifically recommend the following oral antibiotics for impetigo in both pediatric and adult patients 1:

• Cephalexin: 25-50 mg/kg/day divided into 4 doses for 7 days (can be given twice daily for improved compliance) 2, 3
• Dicloxacillin: 25-50 mg/kg/day divided into 4 doses for 7 days 1, 2
• Amoxicillin-clavulanic acid: Provides adequate staphylococcal coverage (unlike amoxicillin alone, which should NOT be used) 1, 2, 4

Critical caveat: Penicillin alone is seldom effective for impetigo and should only be used when cultures confirm streptococci alone, as Staphylococcus aureus is now the predominant causative organism in most cases 2, 4, 5

Alternative Antibiotics for MRSA Coverage

When MRSA is suspected or confirmed, or in geographic areas with high MRSA prevalence, use 1, 2, 4:

• Clindamycin: 20-30 mg/kg/day divided into 3 doses for 7 days 2, 4
• Sulfamethoxazole-trimethoprim (SMX-TMP): 8-12 mg/kg/day (based on trimethoprim component) divided into 2 doses for 7 days 1, 2, 4
• Doxycycline: 2-4 mg/kg/day divided into 2 doses for 7 days (only for children >8 years old due to dental staining risk) 2, 4

Important limitation: SMX-TMP covers MRSA effectively but provides inadequate coverage for streptococcal infections, so consider combination therapy or alternative agents if streptococcal infection is suspected 4

Antibiotics to Avoid

• Penicillin V: Rarely effective due to poor staphylococcal coverage 2, 5
• Amoxicillin alone: Lacks adequate S. aureus coverage 2
• Erythromycin: Rising resistance rates limit its utility, though it remains in IDSA guidelines as an option 1, 4, 5

Treatment Duration and Indications for Oral Therapy

• Standard duration: 7 days for all oral antibiotics (not the 5-day course used for topical agents) 2
• Indications for oral over topical therapy: Numerous lesions, extensive disease, or during outbreaks to decrease transmission 2, 4
• Topical therapy consideration: Mupirocin or retapamulin for 5 days may be superior to oral antibiotics for limited disease 1, 2, 5, 6

Special Populations

• Pregnant patients: Cephalexin is considered safe 2
• Penicillin allergy: Use clindamycin or macrolides (though macrolide resistance is increasing) 2, 4
• Children under 8 years: Avoid tetracyclines (doxycycline) 2

Resistance Patterns and Empiric Considerations

The evidence shows that antibiotic resistance has significantly altered treatment approaches 4:

• Methicillin-resistant S. aureus (MRSA) prevalence is increasing 2, 4
• Macrolide-resistant streptococcus is documented 4
• In areas with high MRSA prevalence, empiric therapy should cover MRSA until culture results are available 2
• All staphylococcal strains in comparative studies showed resistance to penicillin G, supporting avoidance of penicillin monotherapy 3