Cephalexin Dosing for Folliculitis in a 17-Year-Old
For a 17-year-old with armpit folliculitis, administer cephalexin 500 mg orally four times daily (every 6 hours) for 7-10 days. 1, 2
Rationale for This Dosing
At 17 years old, this patient should receive adult dosing since the FDA label specifies adult dosing for patients over 15 years of age, and pediatric dosing guidelines typically transition to adult regimens by mid-adolescence 2
The standard adult dose for skin and soft tissue infections is 500 mg four times daily (every 6 hours), which provides adequate coverage against Staphylococcus aureus and Streptococcus pyogenes, the primary pathogens causing folliculitis 3, 4, 1, 2
Folliculitis is typically caused by S. aureus and presents as papules and pustules in hair-bearing areas like the axilla, making cephalexin an appropriate first-line choice for methicillin-susceptible organisms 5, 6
Treatment Duration and Monitoring
Continue treatment for 7-10 days, as this duration is standard for uncomplicated skin and soft tissue infections 1, 6
Clinical improvement should be evident within 3-5 days; if no improvement occurs, consider alternative diagnoses or resistant organisms 7
Important Clinical Considerations
When Cephalexin May NOT Be Appropriate
If the patient has been shaving the axilla, folliculitis is particularly common in this setting and usually responds well to cephalexin, but counsel on proper shaving technique with adequate lubrication to prevent recurrence 5
If MRSA is suspected (purulent drainage, previous MRSA infection, or failure to respond to β-lactams), switch to agents effective against methicillin-resistant organisms such as trimethoprim-sulfamethoxazole, doxycycline, or clindamycin 4, 1
If gram-negative folliculitis is suspected (patient on prolonged antibiotic therapy for acne, uniform pustules), cephalexin will be ineffective and isotretinoin or alternative antibiotics are required 8
Dosing Schedule
Administer at consistent 6-hour intervals (e.g., 6:00 AM, 12:00 PM, 6:00 PM, 12:00 AM) to maintain therapeutic antibiotic levels 1
The medication can be taken with or without food, though taking with food may reduce gastrointestinal side effects 2
Common Pitfalls to Avoid
Do not use twice-daily dosing for folliculitis—while the FDA label mentions 500 mg every 12 hours for certain infections (streptococcal pharyngitis, uncomplicated cystitis), four-times-daily dosing is recommended for skin infections to maintain adequate tissue concentrations 1, 2
Do not assume all folliculitis is bacterial—if the patient has concurrent acne and has been on long-term antibiotics, consider gram-negative folliculitis or Pityrosporum (fungal) folliculitis, which require different treatments 9, 8
Warn about gastrointestinal side effects, particularly diarrhea, which occurs in approximately 4-8% of patients 10, 7
Alternative Considerations
If the patient has a non-severe penicillin allergy (not anaphylaxis, angioedema, or urticaria), cephalexin can still be used safely 1
For severe penicillin allergies, alternative agents include clindamycin or doxycycline 4
If no improvement after 5 days, reassess for deeper infection, abscess formation, or resistant organisms and consider culture and sensitivity testing 4, 11