Is cephalexin (cephalexin) an appropriate treatment for a patient with impetigo?

Treatment of Impetigo with Cephalexin

Cephalexin is an appropriate first-line treatment for impetigo, as it is effective against both Staphylococcus aureus and Streptococcus pyogenes, the most common causative organisms. 1

Causative Organisms and Treatment Rationale

• Impetigo is typically caused by Staphylococcus aureus and/or Streptococcus pyogenes (Group A Streptococcus) 1
• S. aureus is the predominant pathogen in most cases of impetigo, with studies showing it as the sole pathogen in approximately 62% of cases 2
• Because S. aureus isolates from impetigo are usually methicillin-susceptible, dicloxacillin or cephalexin is recommended as first-line therapy 1
• Cephalexin is FDA-approved for "skin and skin structure infections caused by Staphylococcus aureus and/or Streptococcus pyogenes" 3

Recommended Dosing and Duration

• For impetigo, oral therapy should be a 7-day regimen with an agent active against S. aureus 1
• Typical dosing of cephalexin for impetigo is 500 mg orally three to four times daily for adults 1
• For pediatric patients, the recommended dose is 40-50 mg/kg/day divided into 3-4 doses 2
• Twice-daily dosing of cephalexin has also been shown to be effective for staphylococcal skin infections, which may improve patient compliance 4

Efficacy of Cephalexin

• Clinical studies have demonstrated that cephalexin is highly effective for impetigo, with one study showing no treatment failures in patients treated with cephalexin compared to 24% failure rate with penicillin V 2
• Comparative studies between cephalexin and dicloxacillin have shown equal efficacy for staphylococcal skin infections 4
• Cephalexin has demonstrated excellent activity against both S. aureus and S. pyogenes, the primary pathogens in impetigo 1, 2

Alternative Treatments

• When MRSA is suspected or confirmed, alternative treatments include doxycycline, clindamycin, or sulfamethoxazole-trimethoprim (SMX-TMP) 1
• If cultures yield streptococci alone (which is uncommon), oral penicillin is the recommended agent 1
• Topical mupirocin or retapamulin twice daily for 5 days is also effective for limited impetigo 1, 5
• Systemic therapy is preferred over topical therapy for patients with numerous lesions or in outbreaks affecting several people 1, 5

Special Considerations

• In areas with high prevalence of MRSA, empiric coverage with agents effective against MRSA should be considered if there is no clinical improvement with cephalexin 1
• During outbreaks of post-streptococcal glomerulonephritis, systemic antimicrobials should be used to help eliminate nephritogenic strains of S. pyogenes 1
• Gram stain and culture of pus or exudates from skin lesions can help identify the causative organism, but treatment without these studies is reasonable in typical cases 1

Common Pitfalls

• Failure to recognize MRSA as a potential pathogen in non-responsive cases 1
• Inadequate duration of therapy (less than 7 days) may lead to treatment failure 1
• Using penicillin alone for impetigo is often inadequate due to the high prevalence of S. aureus, which is frequently penicillin-resistant 2
• Not considering systemic therapy for extensive impetigo or during outbreaks, which may lead to continued transmission of infection 1

In conclusion, cephalexin is an appropriate and effective treatment choice for a patient with impetigo, particularly when S. aureus is the suspected or confirmed pathogen.