Minimum Age for Cephalexin Initiation
Cephalexin can be safely initiated in infants as young as 7 days of age, with the FDA-approved pediatric dosing starting at 25-50 mg/kg/day in divided doses for children of all ages. 1
Age-Specific Initiation Guidelines
Neonates and Young Infants (7-60 days)
- Recent pharmacokinetic data from the Journal of the Pediatric Infectious Diseases Society demonstrates that cephalexin achieves adequate therapeutic targets in infants as young as 7 days old when dosed at 25 mg/kg every 6-8 hours. 2
- The FDA label does not specify a minimum age restriction, stating only "pediatric patients" for the 25-50 mg/kg/day dosing range, which has been interpreted to include neonates beyond the first week of life. 1
- Maturational changes in gastrointestinal absorption and renal clearance occur during early infancy, requiring careful attention to post-menstrual age and post-natal age when dosing neonates. 2
Infants and Children (>1 year)
- For streptococcal pharyngitis and skin/skin structure infections in patients over 1 year of age, the FDA approves twice-daily dosing (every 12 hours) as an alternative to four-times-daily administration. 1
- Standard dosing remains 25-50 mg/kg/day in divided doses for most infections. 1
Weight-Based Dosing Schedule
Standard Dosing Algorithm
- For most infections: 25-50 mg/kg/day divided every 6 hours (four times daily) 1
- For streptococcal pharyngitis and skin infections in children >1 year: total daily dose may be divided every 12 hours (twice daily) 1
- For severe infections: dosage may be doubled 1
- For otitis media: 75-100 mg/kg/day in 4 divided doses is required 1
Practical Dosing Examples by Weight
For 125 mg/5 mL suspension (four times daily): 1
- 10 kg child: 0.5-1 teaspoon four times daily
- 20 kg child: 1-2 teaspoons four times daily
- 40 kg child: 2-4 teaspoons four times daily
For 125 mg/5 mL suspension (twice daily): 1
- 10 kg child: 1-2 teaspoons twice daily
- 20 kg child: 2-4 teaspoons twice daily
- 40 kg child: 4-8 teaspoons twice daily
Alternative Reduced-Frequency Dosing
Recent pharmacokinetic modeling supports less frequent dosing to improve adherence: 3, 4
- Three times daily: 45 mg/kg/dose (maximum 1.5 g) for bone and joint infections has demonstrated 99% cure rates in children aged 1-18 years. 3
- Twice daily: 22-45 mg/kg/dose for MSSA with MIC 1-2 mg/L achieves adequate pharmacodynamic targets. 4
Critical Considerations and Pitfalls
Neonatal Dosing Cautions
- Avoid confusing cephalexin with ceftriaxone in neonates—ceftriaxone has specific contraindications in hyperbilirubinemic neonates due to bilirubin displacement, while cephalexin does not carry this risk. 5
- Renal function maturation is incomplete in neonates, requiring attention to post-menstrual age when calculating clearance. 2
- The elimination half-life in neonates (approximately 5 hours) is longer than in older children and adults, supporting less frequent dosing intervals. 2
Duration of Therapy
- For β-hemolytic streptococcal infections: minimum 10 days of therapy is mandatory to prevent rheumatic fever and glomerulonephritis. 1
- Suspension stability: after mixing, refrigerate and discard after 14 days. 1