Cephalexin (Keflex) Dosing and Treatment Duration
For most skin and soft tissue infections in adults, prescribe cephalexin 500 mg four times daily (every 6 hours) for 7-10 days. 1, 2, 3
Adult Dosing Regimens
Standard Infections
- 500 mg four times daily (every 6 hours) is the recommended dose for skin and soft tissue infections caused by methicillin-susceptible Staphylococcus aureus (MSSA) 1, 3, 4
- For mild to moderate infections, 250-500 mg every 6 hours may be sufficient 3, 4
- The FDA-approved dosage range is 1-4 grams daily in divided doses 4
Alternative Dosing for Specific Conditions
- 500 mg twice daily (every 12 hours) can be used for streptococcal pharyngitis, uncomplicated skin infections, and uncomplicated cystitis in patients over 15 years 4
- For uncomplicated cystitis, continue therapy for 7-14 days 4
Severe Infections
- For more severe infections or less susceptible organisms, higher doses may be needed 4
- If daily doses exceeding 4 grams are required, switch to parenteral cephalosporins 4
Pediatric Dosing
Standard Pediatric Regimen
- 25-50 mg/kg/day divided into 4 doses for mild to moderate infections 3, 4
- For streptococcal pharyngitis and skin infections in children over 1 year, the total daily dose may be divided and given every 12 hours 4
MSSA Infections in Children
- 75-100 mg/kg/day divided into 3-4 doses for methicillin-susceptible Staphylococcus aureus infections 1, 3
- For otitis media, 75-100 mg/kg/day in 4 divided doses is required 4
Treatment Duration
- 7-10 days is the typical duration for most infections, depending on clinical response 2, 3
- For uncomplicated skin infections, 7 days is standard 2
- If no improvement within 5 days, extend treatment duration 2
- For β-hemolytic streptococcal infections, administer for at least 10 days 4
Critical Pitfalls to Avoid
MRSA Coverage
- Cephalexin is NOT effective against MRSA 1, 2, 3
- If MRSA is suspected or confirmed, switch to trimethoprim-sulfamethoxazole, doxycycline, or clindamycin 1, 3
Limited Pathogen Coverage
- Cephalexin lacks activity against Pasteurella multocida (important for animal bites) and most anaerobes 1, 2
- Not effective for infections requiring anaerobic coverage 1
Penicillin Allergy Cross-Reactivity
- Patients with immediate hypersensitivity reactions to penicillin should avoid cephalexin due to potential cross-reactivity 1, 2
- For non-immediate reactions, cephalexin remains appropriate 1
Special Clinical Situations
Mastitis in Lactating Women
- 500 mg orally every 6 hours (four times daily) for lactating women with mastitis 3
- Cephalexin achieves therapeutic levels in breast milk and is safe for nursing infants 3