Medication Dosing for Impetigo
For impetigo, adults should receive dicloxacillin 250 mg four times daily or cephalexin 250 mg four times daily orally for 7 days, while children should receive dicloxacillin 12 mg/kg/day or cephalexin 25 mg/kg/day in 4 divided doses orally for 7 days. 1
Treatment Algorithm by Disease Extent
Limited Lesions (Topical Therapy)
For patients with a limited number of lesions, topical mupirocin ointment applied to lesions three times daily is the preferred first-line treatment 1. This recommendation is particularly strong (A-I evidence) and applies to both adults and children, including those with minor skin infections and secondarily infected lesions 2.
- Mupirocin 2% ointment: Apply to lesions 3 times daily for 7 days 1
- Alternative topical option: Retapamulin ointment applied twice daily 3, 4
Widespread Lesions (Systemic Therapy)
When patients have numerous lesions or fail to respond to topical agents, oral antimicrobials are indicated 1:
First-Line Oral Antibiotics (for methicillin-susceptible strains):
Adults:
- Dicloxacillin: 250 mg four times daily orally 1
- Cephalexin: 250 mg four times daily orally 1
- Amoxicillin-clavulanate: 875/125 mg twice daily orally 1
Children:
- Dicloxacillin: 12 mg/kg/day in 4 divided doses orally 1
- Cephalexin: 25-50 mg/kg/day in 3-4 divided doses orally 3, 4
- Amoxicillin-clavulanate: 25 mg/kg/day (of amoxicillin component) in 2 divided doses orally 1
Alternative Options:
Adults:
- Clindamycin: 300-400 mg four times daily orally 1, 3
- Erythromycin: 250 mg four times daily orally (or 400 mg four times daily for ethylsuccinate formulation) 1
Children:
- Clindamycin: 20 mg/kg/day in 3 divided doses orally 3, 4
- Erythromycin: 40 mg/kg/day in 3-4 divided doses orally 1, 3
MRSA-Suspected or Confirmed Cases
When MRSA is suspected or confirmed, adjust therapy to 3:
Adults:
- Doxycycline: 100 mg twice daily orally
- Clindamycin: 300-400 mg four times daily orally
- TMP-SMX: 1-2 double-strength tablets twice daily orally
Children:
- Clindamycin: 20 mg/kg/day in 3 divided doses orally
- TMP-SMX: 8-12 mg/kg/day (based on trimethoprim component) in 2 divided doses orally
- Note: Doxycycline is not recommended for children <8 years of age 1, 3
Duration of Therapy
All treatment regimens should be continued for approximately 7 days, depending on clinical response 1. The 2014 IDSA guidelines specifically recommend a 7-day regimen for oral therapy 3.
Important Clinical Caveats
Resistance patterns matter: Erythromycin resistance has been increasing, with some strains of S. aureus and S. pyogenes showing resistance 1. Approximately 50% of MRSA strains have inducible or constitutive clindamycin resistance 1. When prescribing clindamycin for suspected MRSA, ensure local resistance rates are low (ideally <10%) 2.
Mupirocin resistance: While mupirocin remains highly effective (A-I evidence), resistance has been described and should be considered if treatment fails 1.
Penicillin V is inadequate: Historical data show treatment failure rates of 24% with penicillin V compared to 4% with erythromycin and 0% with cephalexin 5. Therefore, penicillin V should not be used as monotherapy for impetigo.
Re-evaluation is essential: If patients are treated with empirical therapy and sent home, they should be re-evaluated in 24-48 hours to verify clinical response, particularly when using agents with documented resistance patterns 1.