What are the best oral antibiotics for treating impetigo?

Best Oral Antibiotics for Impetigo

For impetigo, dicloxacillin or cephalexin are the first-line oral antibiotics for methicillin-susceptible Staphylococcus aureus (MSSA), while clindamycin, trimethoprim-sulfamethoxazole (TMP-SMZ), or doxycycline (for patients ≥8 years) should be used when methicillin-resistant S. aureus (MRSA) is suspected. 1

Causative Organisms and Antibiotic Selection

Impetigo is primarily caused by:

• Staphylococcus aureus (most common)
• Streptococcus pyogenes (Group A streptococcus)
• Mixed infections with both organisms

First-line oral antibiotics for MSSA:

1. Dicloxacillin

   • Adult dosage: 250-500 mg 4 times per day 2
   • Pediatric dosage: 12.5-25 mg/kg/day in 4 divided doses 2
   • Advantages: Excellent oral agent for methicillin-susceptible strains 2

2. Cephalexin

   • Adult dosage: 250-500 mg 4 times per day 2
   • Pediatric dosage: 25 mg/kg/day in 4 divided doses 2
   • Advantages: Suitable for penicillin-allergic patients (except those with immediate hypersensitivity reactions) 2
   • Research shows cephalexin twice daily may be as effective as dicloxacillin four times daily, potentially improving compliance 3

For suspected or confirmed MRSA:

1. Clindamycin

   • Adult dosage: 300-450 mg 3 times per day 2
   • Pediatric dosage: 10-20 mg/kg/day in 3 divided doses 2
   • Caution: Potential for cross-resistance with erythromycin and inducible resistance in MRSA 2

2. Trimethoprim-Sulfamethoxazole (TMP-SMZ)

   • Adult dosage: 1-2 double-strength tablets twice per day 2
   • Pediatric dosage: 8-12 mg/kg/day (based on trimethoprim) in 2 divided doses 2
   • Note: Effective against MRSA but may have inadequate coverage for streptococcal infections 4

3. Doxycycline

   • Adult dosage: 100 mg twice per day 2
   • Not recommended for children under 8 years of age 2, 1

Treatment Duration and Monitoring

• Standard duration: 7 days, depending on clinical response 2, 1
• Evaluate clinical response within 48-72 hours
• Consider alternative antibiotics if no improvement within 3-5 days 1

Special Considerations

Penicillin Allergy

• For non-immediate hypersensitivity: Cephalexin is appropriate
• For immediate hypersensitivity reactions: Clindamycin or TMP-SMZ

Pediatric Patients

• Avoid tetracyclines (doxycycline, minocycline) in children under 8 years 2, 1
• Dicloxacillin should be taken on an empty stomach, at least 1 hour before or 2 hours after meals 5

When to Consider Topical Treatment Instead

• For limited, localized lesions, topical mupirocin is effective 2, 1
• Apply to lesions 3 times daily for 5-7 days 2, 1

Common Pitfalls to Avoid

1. Using penicillin alone

   • Penicillin V is inadequate for impetigo treatment due to high rates of penicillin-resistant S. aureus 6
   • Studies show treatment failure rates of 24% with penicillin V compared to 0% with cephalexin 6

2. Failing to consider MRSA

   • If no improvement with first-line therapy, consider MRSA and switch to appropriate antibiotics

3. Inadequate duration of therapy

   • Complete the full 7-day course even if symptoms improve quickly

4. Relying solely on oral therapy for extensive disease without culture

   • Obtain cultures from active lesions to guide therapy in severe or recurrent cases 1

Conclusion

For most cases of impetigo, dicloxacillin or cephalexin remain the oral antibiotics of choice when MRSA is not suspected. For suspected or confirmed MRSA infections, clindamycin, TMP-SMZ, or doxycycline (in patients ≥8 years) are appropriate alternatives. The standard duration of therapy is 7 days, with clinical response expected within 48-72 hours of initiating appropriate treatment.