What oral antibiotics are recommended for a patient with impetigo, considering potential penicillin allergy?

Oral Antibiotics for Impetigo

For impetigo requiring oral therapy, cephalexin (25-50 mg/kg/day divided into 4 doses for 7 days) is the first-line oral antibiotic, with clindamycin or sulfamethoxazole-trimethoprim as preferred alternatives when MRSA is suspected or in penicillin-allergic patients. 1

When Oral Antibiotics Are Indicated

Oral antibiotics should be used instead of topical therapy when: 1, 2

• Extensive disease with numerous lesions is present
• Failure to respond to topical therapy after 3-5 days
• Systemic symptoms are present
• Lesions on the face, eyelid, or mouth require systemic treatment
• During outbreaks to decrease transmission 1

First-Line Oral Antibiotic Options

For Presumed Methicillin-Susceptible S. aureus (MSSA):

Cephalexin is the preferred first-line agent: 1

• Pediatric dosing: 25-50 mg/kg/day divided into 4 doses
• Adult dosing: 250-500 mg four times daily 2
• Duration: 7 days 1

Dicloxacillin is an alternative first-line option: 1, 2

• Pediatric dosing: 25-50 mg/kg/day divided into 4 doses
• Adult dosing: 250 mg four times daily 2
• Duration: 7 days 1

Co-amoxiclav (amoxicillin-clavulanate) is an acceptable alternative that provides coverage for both S. aureus and S. pyogenes: 1, 3

• Duration: 7 days 1

Penicillin-Allergic Patients

For patients with penicillin allergy, clindamycin is the preferred alternative: 2

• Pediatric dosing: 20-30 mg/kg/day divided into 3 doses 1
• Adult dosing: 300-450 mg three times daily 2
• Duration: 7 days 1

Important caveat: Avoid cephalosporins (like cephalexin) if the patient has a type 1 hypersensitivity reaction (anaphylaxis/hives) to β-lactams. 2 However, cephalexin can be used in patients with non-severe penicillin allergies. 4

Alternative options for penicillin allergy include: 4

• Clarithromycin (macrolide)
• Azithromycin (macrolide)

Critical warning: Resistance rates to erythromycin and other macrolides are rising, limiting their utility. 1, 3

When MRSA Is Suspected

In areas with high MRSA prevalence or when MRSA is suspected, empiric therapy should cover MRSA: 1

Clindamycin: 1, 2

• Pediatric: 20-30 mg/kg/day divided into 3 doses
• Adult: 300-450 mg three times daily
• Duration: 7 days

Sulfamethoxazole-trimethoprim (SMX-TMP): 1, 2

• Pediatric: 8-12 mg/kg/day (based on trimethoprim component) divided into 2 doses
• Adult: 1-2 double-strength tablets twice daily
• Duration: 7 days
• Important limitation: Inadequate for streptococcal infection 3

Doxycycline: 1, 3

• Only for children over 8 years old (risk of permanent dental staining) 1
• Pediatric (>8 years): 2-4 mg/kg/day divided into 2 doses
• Duration: 7 days

Antibiotics That Should NOT Be Used

Penicillin alone is seldom effective and should only be used when cultures confirm streptococci alone. 1, 2 Penicillin was consistently inferior to other antibiotics in comparative trials. 5, 6

Amoxicillin alone should not be used because it lacks adequate coverage against S. aureus, which is now the predominant causative organism. 1

Erythromycin has shown inferior efficacy compared to topical mupirocin and other oral antibiotics, and resistance is increasing. 7, 6

Treatment Duration

The standard duration for oral antibiotic therapy is 7 days, not the shorter 5-day course used for topical agents. 1, 2 This longer duration is necessary to avoid treatment failure. 1

Special Populations

Pregnant patients: Cephalexin is considered a safe alternative. 1

Immunocompromised patients: 2

• Lower threshold for oral antibiotics
• Monitor closely for treatment failure or deeper infection
• Consider longer treatment duration based on clinical response

Athletes: Should be excluded from participation until 24 hours after initiation of effective antimicrobial therapy, with lesions covered by clean, dry bandages. 2

Common Pitfalls to Avoid

• Do not use topical clindamycin cream for impetigo—it lacks FDA indication and has insufficient systemic absorption for bacterial skin infections. 1
• Do not use disinfectant solutions as primary therapy—there is little evidence they improve outcomes. 1, 6
• Do not prescribe oral antibiotics for limited disease when topical mupirocin is appropriate and more effective. 1
• Obtain cultures if there is treatment failure, MRSA is suspected, or in cases of recurrent infections. 2

Monitoring and Follow-Up

If no improvement occurs by 3-5 days of appropriate therapy, reassess for: 2

• MRSA infection requiring alternative antibiotics
• Deeper or more complex infection than initially estimated
• Non-compliance with therapy
• Antibiotic resistance