Cephalexin Three Times Daily Dosing
For adults, cephalexin dosed three times daily should be 500 mg per dose (1500 mg total daily), and for children, 25 mg/kg per dose (maximum 750 mg per dose) is appropriate for most infections.
Adult Dosing
The FDA-approved dosing for cephalexin allows flexibility in administration frequency 1. While the standard adult dose is 250 mg every 6 hours (four times daily), 500 mg every 12 hours (twice daily) is explicitly approved for streptococcal pharyngitis, skin and skin structure infections, and uncomplicated cystitis 1.
For three times daily dosing in adults:
- Standard dose: 500 mg three times daily (1500 mg total daily dose)
- This falls well within the FDA-approved range of 1-4 grams daily in divided doses 1
- More severe infections may require higher doses, but if exceeding 4 grams daily, parenteral cephalosporins should be considered 1
Pediatric Dosing
The evidence strongly supports three times daily dosing in children:
For most pediatric infections, use 25 mg/kg per dose three times daily (maximum 750 mg per dose) 2, 3. This dosing regimen:
- Achieves the same pharmacodynamic targets as traditional four times daily dosing 2
- Demonstrated 99% cure rates (147/149 patients) in children with bone and joint infections 2
- Improves adherence by reducing dosing frequency from four to three times daily
For more serious infections (bone and joint infections, severe skin infections), use 45 mg/kg per dose three times daily (maximum 1500 mg per dose) 2. This higher dose:
- Was effective and well-tolerated in 149 children with bone and joint infections 2
- Minimal side effects: only 4 children had GI symptoms, 13 developed mild neutropenia without complications 2
Important Caveats
Infection-Specific Considerations
- Otitis media requires higher dosing: 75-100 mg/kg/day divided into 4 doses 1
- Streptococcal infections: Must treat for at least 10 days regardless of dosing frequency 1
- Cystitis: Continue therapy for 7-14 days 1
Dosing Frequency Trade-offs
Recent evidence suggests that less frequent dosing (twice or three times daily) may improve adherence without compromising efficacy 2, 4. A study of UTIs found no statistically significant difference in treatment failure between twice daily (18.7%) versus four times daily (15.0%) dosing 4.
Storage and Preparation
- Oral suspension must be refrigerated after mixing 1
- Remains stable for 14 days after reconstitution 1
The shift toward three times daily dosing represents a practical, evidence-based approach that balances pharmacokinetic/pharmacodynamic principles with real-world adherence challenges, particularly important in pediatric populations.