Cephalexin Dosing for Soft Tissue Injury
For adults with soft tissue infections, cephalexin should be dosed at 500 mg orally four times daily (every 6 hours) for 7 days, or alternatively 500 mg every 12 hours for uncomplicated cases. 1
Adult Dosing Regimens
The FDA-approved dosing provides two options depending on infection severity:
- Standard dosing: 250 mg every 6 hours for routine infections 1
- Moderate infections: 500 mg every 12 hours for skin and soft tissue infections 1
- More severe infections: 500 mg four times daily (every 6 hours), which may be necessary for less susceptible organisms 1
The IDSA guidelines specifically recommend cephalexin at 75-100 mg/kg/day divided into 3-4 doses for pediatric patients with methicillin-susceptible Staphylococcus aureus infections 2, and this translates to the 500 mg four times daily regimen for adults in clinical practice 3.
Pediatric Dosing
For children with soft tissue infections:
- Standard dose: 25-50 mg/kg/day divided into four doses 1
- Alternative: Total daily dose may be divided every 12 hours for skin and soft tissue infections 1
- Severe infections: Dosage may be doubled 1
The IDSA guidelines recommend 75-100 mg/kg/day in 3-4 divided doses for methicillin-susceptible staphylococcal infections 2.
Duration of Therapy
- Standard duration: 7 days for uncomplicated soft tissue infections 3, 4
- Extended therapy: If no improvement by day 5, extend treatment duration 3
- Clinical monitoring: Reassess at 72 hours for treatment failure 4
Microbiological Coverage
Cephalexin provides excellent activity against the most common soft tissue pathogens:
- Effective against: Methicillin-susceptible Staphylococcus aureus and Streptococcus species 2, 3
- Not effective against: MRSA, Pasteurella multocida, and most anaerobes 3
Critical Pitfalls to Avoid
MRSA consideration: If MRSA is suspected (risk factors include prior MRSA infection, injection drug use, recent hospitalization), cephalexin is inadequate and alternative agents such as trimethoprim-sulfamethoxazole, doxycycline, or clindamycin should be used instead 2, 3. A recent high-quality trial demonstrated that adding trimethoprim-sulfamethoxazole to cephalexin did not significantly improve outcomes for uncomplicated cellulitis, though the confidence intervals included potential benefit 5.
Penicillin allergy: Patients with immediate hypersensitivity reactions to penicillin should avoid cephalexin due to potential cross-reactivity 3. However, for non-immediate reactions, cephalexin remains an appropriate alternative 2.
Abscess exclusion: Ensure no underlying abscess is present, as antibiotics alone are insufficient without drainage 4. Ultrasound may be warranted if clinical examination is equivocal 4.
Clinical Equivalence Data
A well-designed non-inferiority trial demonstrated that oral cephalexin 500 mg four times daily was equivalent to intravenous cefazolin 2g daily plus oral probenecid for uncomplicated mild-moderate soft tissue infections, with treatment failure rates of 4.2% vs 6.1% respectively 4. This supports outpatient oral therapy as first-line management.