What is the appropriate cephalexin dosage for treating non‑bullous impetigo in children and adults, and what alternatives should be used if there is a penicillin/cephalosporin allergy or suspected MRSA?

Cephalexin for Impetigo Treatment

Recommended Dosing Regimen

For non-bullous impetigo, cephalexin is a first-line oral antibiotic at 250 mg four times daily in adults and 25-50 mg/kg/day divided into 3-4 doses in children for 7 days, covering both Staphylococcus aureus and Streptococcus pyogenes. 1

Adult Dosing

• Cephalexin 250 mg orally four times daily for 7 days 1
• Alternative: 500 mg four times daily for more extensive disease 1

Pediatric Dosing

• Cephalexin 25-50 mg/kg/day divided into 3-4 doses orally for 7 days 1, 2
• The availability of a suspension formulation and less frequent dosing compared to dicloxacillin makes cephalexin particularly practical for children 1

When to Use Topical Therapy Instead

For limited impetigo (few lesions), topical mupirocin 2% ointment applied twice daily for 5 days is superior to oral antibiotics and should be used first-line. 1, 2

• Topical therapy achieves cure rates 6-fold higher than placebo for limited disease 2
• Reserve oral antibiotics like cephalexin for patients with numerous lesions or during outbreaks to decrease transmission 2

Alternatives for MRSA Coverage

If MRSA is suspected based on local epidemiology, purulent drainage, or treatment failure, switch to clindamycin, trimethoprim-sulfamethoxazole, or doxycycline (>8 years old) rather than continuing cephalexin. 1, 2

MRSA-Active Alternatives

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

Managing Penicillin/Cephalosporin Allergy

For patients with penicillin allergy, cephalexin can still be used except in those with immediate hypersensitivity reactions (anaphylaxis, angioedema, urticaria); in such cases, use clindamycin as the alternative. 1, 2

• Cephalexin has <5% cross-reactivity with penicillins in non-immediate hypersensitivity 1
• For documented immediate hypersensitivity: clindamycin 300-450 mg three to four times daily (adults) or 20-30 mg/kg/day in 3 divided doses (children) 2

Critical Treatment Considerations

Duration of Therapy

• All oral antibiotics require 7 days of treatment, not the shorter 5-day course used for topical agents 2
• Shorter courses risk treatment failure and recurrence 2

Agents to Avoid

• Penicillin alone is seldom effective and should only be used when cultures confirm streptococci alone 2
• Amoxicillin alone lacks adequate coverage against S. aureus, which is now the predominant causative organism 2
• Tetracyclines (doxycycline) must be avoided in children under 8 years due to permanent dental staining risk 1, 2

Practical Dosing Alternatives

While four-times-daily dosing is guideline-recommended, twice-daily or three-times-daily cephalexin regimens may improve adherence and are supported by pharmacokinetic data. 3, 4

• For twice-daily dosing: 22-45 mg/kg/dose for MSSA with MIC 1-2 mg/L 3
• For three-times-daily dosing: 15-25 mg/kg/dose for MSSA with MIC 1-2 mg/L 3
• A 1983 study demonstrated twice-daily cephalexin was equally effective as four-times-daily dicloxacillin for staphylococcal skin infections 4

Infection Control Measures

Implement concurrent hygiene measures to prevent spread and recurrence: 1, 2

• Keep draining wounds covered with clean, dry bandages 1, 2
• Maintain regular handwashing with soap and water or alcohol-based gel 1
• Avoid sharing personal items (razors, linens, towels) that contact infected skin 1
• Clean high-touch surfaces (counters, doorknobs, bathtubs) that contact bare skin 1

Common Pitfalls to Avoid

• Do not prescribe oral antibiotics for limited disease when topical mupirocin is appropriate and more effective 2
• Do not use cephalexin when MRSA is documented or strongly suspected—it lacks MRSA coverage 2
• Do not use treatment durations shorter than 7 days for oral therapy 2
• Do not assume cephalexin covers MRSA in areas with high community-acquired MRSA prevalence 1