Yes, Keflex (cephalexin) effectively treats impetigo
Cephalexin is explicitly recommended by the IDSA guidelines as a first-line oral antibiotic for impetigo caused by Staphylococcus and Streptococcus species 1.
Dosing Recommendations
According to the 2014 IDSA guidelines for skin and soft tissue infections 1:
Adults:
- Cephalexin 250 mg four times daily orally
Children:
- 25-50 mg/kg/day divided into 3-4 doses orally
Treatment duration: 7 days, depending on clinical response
Why Cephalexin Works for Impetigo
Impetigo is primarily caused by:
- Staphylococcus aureus (most common, ~62% of cases) 2
- Group A Streptococcus (Streptococcus pyogenes)
- Mixed infections with both organisms (~19% of cases) 2
Cephalexin provides excellent coverage against both pathogens. Clinical studies demonstrate:
- 98.3% clinical cure rate in pediatric impetigo patients 3
- Microbiologic eradication in 99.4% of isolated pathogens 3
- Superior to penicillin V, which had a 24% treatment failure rate compared to 0% with cephalexin 2
Clinical Considerations
When to use oral antibiotics (like cephalexin) versus topical therapy:
- Use cephalexin for severe or multilesional impetigo that doesn't respond to topical therapy within 3-5 days 4
- Use cephalexin for outbreak situations to decrease transmission 4
- For limited lesions, topical mupirocin or retapamulin ointment are preferred initial treatments 1, 4
Advantages of cephalexin:
- Availability as a suspension makes it practical for pediatric use 1
- Less frequent dosing than some alternatives improves compliance 1
- Effective against both MSSA and streptococci 1
- Well-tolerated with low adverse event rates 3
Important Caveats
⚠️ MRSA consideration: If MRSA is suspected (based on local resistance patterns, previous MRSA infection, or treatment failure), cephalexin will NOT be effective. Consider clindamycin, trimethoprim-sulfamethoxazole, or doxycycline instead 1.
⚠️ Penicillin allergy: Cephalexin can be used in penicillin-allergic patients except those with immediate hypersensitivity reactions (anaphylaxis, urticaria) 1.
⚠️ Drug interaction: Monitor patients on metformin closely, as cephalexin increases metformin levels by ~34% 5.