Recommended Antibiotic for Bullous Impetigo
For bullous impetigo, use oral 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 therapy, since bullous impetigo is exclusively caused by Staphylococcus aureus and these agents provide optimal anti-staphylococcal coverage. 1, 2
Understanding Bullous Impetigo
Bullous impetigo is distinctly different from non-bullous impetigo because it is exclusively caused by toxin-producing Staphylococcus aureus, not streptococci. 2 This pathogen-specific etiology makes treatment selection straightforward—you need anti-staphylococcal coverage.
First-Line Oral Antibiotic Options
For presumed methicillin-susceptible S. aureus (MSSA), which represents the majority of community-acquired cases:
- Cephalexin: 25-50 mg/kg/day divided into 4 doses for 7 days 1, 2
- Dicloxacillin: 25-50 mg/kg/day divided into 4 doses for 7 days 1, 2
Both agents are equally effective and the choice between them is largely based on availability and tolerability. 2
When to Suspect MRSA and Adjust Therapy
In areas with high MRSA prevalence or when MRSA is suspected/confirmed, switch to:
- Clindamycin: 20-30 mg/kg/day divided into 3 doses for 7 days 1, 2
- Trimethoprim-sulfamethoxazole (SMX-TMP): 8-12 mg/kg/day (based on trimethoprim component) divided into 2 doses for 7 days 1, 2
- Doxycycline (for children >8 years): 2-4 mg/kg/day divided into 2 doses for 7 days 2
Critical caveat: Trimethoprim-sulfamethoxazole provides excellent MRSA coverage but has inadequate streptococcal coverage. 3 However, since bullous impetigo is caused exclusively by S. aureus, this limitation is not relevant for this specific condition. 2
Why Topical Therapy Is Insufficient
Unlike non-bullous impetigo where topical mupirocin may suffice for limited disease, bullous impetigo typically requires systemic oral antibiotics because the large, flaccid bullae indicate deeper tissue involvement and toxin-mediated disease. 2, 3 The bullae are caused by exfoliative toxins produced by S. aureus, necessitating systemic antimicrobial therapy to address both the infection and toxin production.
Antibiotics to Avoid
Never use penicillin alone for impetigo—it lacks adequate coverage against S. aureus, which is universally the causative organism in bullous impetigo. 4, 3
Treatment Duration and Monitoring
- Standard duration: 7 days of oral antibiotic therapy 1, 2
- Obtain cultures if there is treatment failure, MRSA is suspected, or in cases of recurrent infections 4
- Clinical improvement should be evident within 3-5 days; if not, reassess for MRSA or treatment adherence 4