What is the best antibiotic for treating severe impetigo?

Best Antibiotic for Severe Impetigo

For severe impetigo requiring systemic therapy, 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 are the first-line antibiotics, with clindamycin (20-30 mg/kg/day divided into 3 doses) or trimethoprim-sulfamethoxazole (8-12 mg/kg/day based on TMP component divided into 2 doses) reserved for suspected MRSA. 1

When to Use Systemic vs. Topical Therapy

• Systemic oral antibiotics are indicated when patients have numerous lesions, extensive disease, or during outbreaks to decrease transmission 1
• Topical mupirocin or retapamulin is reserved for limited impetigo with few lesions 1
• Severe impetigo by definition requires oral therapy due to the extent of involvement 2, 1

First-Line Oral Antibiotic Selection

For Methicillin-Susceptible S. aureus (MSSA)

• Cephalexin 250 mg four times daily (adults) or 25-50 mg/kg/day divided into 4 doses (children) for 7 days 2, 1
• Dicloxacillin 250 mg four times daily (adults) or 25-50 mg/kg/day divided into 4 doses (children) for 7 days 2, 1, 3
• Both agents are equally effective, but cephalexin may be preferred due to twice-daily dosing options that enhance compliance 4
• Cephalexin demonstrated superior efficacy compared to penicillin V (0% vs 24% treatment failure) and equal efficacy to erythromycin in clinical trials 5

Critical Point About Penicillin

• Penicillin V is seldom effective for impetigo and should only be used when cultures confirm streptococci alone 1
• This is because Staphylococcus aureus is now the predominant causative organism (62% S. aureus alone, 19% mixed S. aureus and streptococci) 5
• Amoxicillin alone should not be used as it lacks adequate coverage against S. aureus 1

When to Cover for MRSA

Indications for MRSA Coverage

• High MRSA prevalence in your geographic area 1
• Failure to respond to beta-lactam therapy 2
• Systemic toxicity or signs of severe infection 2

MRSA-Active Oral Antibiotics

• Clindamycin 300-400 mg three times daily (adults) or 20-30 mg/kg/day divided into 3 doses (children) for 7 days 2, 1
• Trimethoprim-sulfamethoxazole (TMP-SMX) 1-2 double-strength tablets twice daily (adults) or 8-12 mg/kg/day based on TMP component divided into 2 doses (children) for 7 days 2, 1
• Doxycycline 100 mg twice daily (adults) or 2-4 mg/kg/day divided into 2 doses (children >8 years) for 7 days 2, 1

Important Caveats for MRSA Coverage

• Clindamycin should only be used empirically if local clindamycin resistance rates are low (e.g., <10%) 2
• TMP-SMX provides excellent MRSA coverage but inadequate streptococcal coverage, so consider adding a beta-lactam (e.g., amoxicillin) if streptococcal infection is suspected 2, 6
• Tetracyclines (doxycycline) must be avoided in children under 8 years due to dental staining risk 2, 1

Treatment Duration and Administration

• Standard duration for all oral antibiotic therapy is 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 3
• Therapy should continue for at least 48 hours after the patient becomes afebrile and asymptomatic 3

Hospitalized Patients with Severe Complicated SSTI

For hospitalized patients with severe impetigo requiring IV therapy:

• IV vancomycin 30 mg/kg/day in 2 divided doses (adults) or 40 mg/kg/day in 4 divided doses (children) 2
• IV clindamycin 600 mg every 8 hours (adults) or 25-40 mg/kg/day in 3 divided doses (children) 2
• IV linezolid 600 mg twice daily (adults and children >12 years) or 10 mg/kg every 8 hours (children <12 years) 2
• IV daptomycin 4 mg/kg once daily (adults only) 2

Common Pitfalls to Avoid

• Never use rifampin as monotherapy or adjunctive therapy for impetigo 2
• Do not use topical disinfectants—they are inferior to antibiotics 6, 7
• Avoid erythromycin due to rising resistance rates 2, 1, 7
• Do not use penicillin V or amoxicillin alone as they lack adequate S. aureus coverage 1, 5
• Always obtain cultures in severe cases to guide definitive therapy and monitor local resistance patterns 3