Cephalexin Dosing for Cellulitis
For adult patients with cellulitis, the recommended dosage of cephalexin (Keflex) is 500 mg orally 3-4 times daily for 5-6 days. 1
Adult Dosing Guidelines
- Standard adult dosing: 500 mg orally 3-4 times daily 1, 2
- Alternative dosing: 1 gram every 12 hours 2
- Total daily dose: 1-4 grams divided throughout the day 2
- Duration: 5-6 days is typically sufficient if clinical improvement occurs 1
The FDA-approved dosing for adults ranges from 1 to 4 grams daily in divided doses, with the usual adult dose being 250 mg every 6 hours. However, for skin and skin structure infections like cellulitis, 500 mg administered every 6-8 hours (3-4 times daily) is the recommended dosage 2.
Pediatric Dosing Guidelines
For pediatric patients with cellulitis, the recommended dosage is:
- 75-100 mg/kg/day divided into 3-4 doses 3, 2
- For children, the usual recommended daily dosage is 25-50 mg/kg in divided doses, but for skin infections, the higher range (75-100 mg/kg/day) is preferred 2
Treatment Considerations
Causative Organisms
Cephalexin is particularly effective against methicillin-susceptible Staphylococcus aureus (MSSA) and beta-hemolytic streptococci, which are the most common causative organisms in non-purulent cellulitis 1, 4.
Treatment Duration
While traditional treatment courses were 7-10 days, recent evidence suggests that a 5-day course is as effective as a 10-day course if clinical improvement has occurred by day 5 1. For streptococcal infections, a full 10-day course is still recommended 2.
Monitoring and Follow-up
- Reassess patients within 48-72 hours of initiating therapy 1
- If no improvement or worsening occurs within 48-72 hours, consider changing to MRSA-active therapy 1
- Complete the full course of antibiotics even if symptoms improve quickly to prevent treatment failure and antibiotic resistance 1
Special Considerations
MRSA Concerns
If MRSA is suspected (e.g., in cases with purulent drainage, previous MRSA infection, or failure to respond to beta-lactam therapy), alternative antibiotics or combination therapy may be needed 1, 5.
High-Dose Option
A recent pilot study suggests that high-dose cephalexin (1000 mg four times daily) may result in fewer treatment failures compared to standard-dose (500 mg four times daily), though with slightly more minor adverse effects 6. However, this was a small pilot study and the standard dose remains the recommended approach until larger studies confirm these findings.
Potential Adverse Effects
Cephalexin is generally well-tolerated with minimal side effects:
- Gastrointestinal effects (diarrhea, nausea) are the most common 4
- Low incidence of allergic reactions due to its stability and chemical configuration 7
- Does not significantly disturb lower bowel flora as it is absorbed high in the intestinal tract 7
Dosage Adjustments
For patients with renal impairment (creatinine clearance less than 30 ml/min), dosage reduction proportional to the reduced renal function is required 7.
Remember that cephalexin is rapidly cleared from the body by the kidneys, with 70-100% of the dose found in the urine 6-8 hours after administration, making it particularly effective for urinary tract infections but requiring dose adjustments in renal impairment 7.