Cephalexin 40 mg/kg/day Should Not Be Started From Birth
Cephalexin is not appropriate for newborns from birth, and 40 mg/kg/day is below the recommended dosing for any age group where cephalexin is indicated. The FDA label specifies the usual pediatric dosage as 25-50 mg/kg/day in divided doses, but this does not apply to the immediate neonatal period 1.
Age-Specific Contraindications
Newborns Under 28 Days
- For infants 8-28 days old with serious infections (UTI, suspected bacteremia), parenteral therapy with ampicillin plus either ceftazidime or gentamicin is the standard of care, not oral cephalexin 2
- Oral cephalexin is inappropriate for infants under 28 days old or those with serious infections requiring hospitalization such as meningitis or bacteremia without identified source 2
- The evidence base for cephalexin pharmacokinetics begins at 7 days of age, not from birth 3
Infants 29-60 Days
- For this age group with urinary tract infections, cephalexin can be used at 50-100 mg/kg/day divided into 4 doses as oral step-down therapy after initial parenteral treatment 2
- This is substantially higher than the proposed 40 mg/kg/day dose
Correct Dosing When Cephalexin Is Appropriate
Standard Pediatric Dosing (After Neonatal Period)
- The usual recommended daily dosage is 25-50 mg/kg/day in divided doses 1
- For streptococcal pharyngitis and skin/skin structure infections in patients over 1 year of age, the total daily dose may be divided every 12 hours 1
- For otitis media, clinical studies require 75-100 mg/kg/day in 4 divided doses 1
Indication-Specific Dosing
- For MSSA infections including community-acquired pneumonia, the recommended dose is 75-100 mg/kg/day divided into 3 or 4 doses 2
- Recent pharmacokinetic data in infants 7-60 days old supports 25 mg/kg/dose every 6-8 hours depending on the pathogen and pharmacodynamic target 3
Critical Pitfalls to Avoid
- The 40 mg/kg/day dose is inadequate even when cephalexin is appropriate - it falls below the minimum 50 mg/kg/day needed for most infections 2, 1
- Maturational changes in gastrointestinal absorption and kidney function during early infancy complicate dosing extrapolation from older populations 3
- For β-hemolytic streptococcal infections, therapeutic dosage must be administered for at least 10 days 1
- In severe infections, the dosage may need to be doubled from standard recommendations 1
Alternative Appropriate Neonatal Antibiotics
When treating neonates from birth, consider these evidence-based alternatives:
- Ampicillin: For neonates with gestational age >34 weeks and postnatal age >7 days, use 75 mg/kg/dose IV every 12 hours 4
- Gentamicin: Dosing varies by gestational and postnatal age, ranging from 4-5 mg/kg/dose with extended intervals 4
- Ceftazidime: For neonates with gestational age ≥32 weeks and postnatal age >7 days, use 50 mg/kg/dose IV every 8 hours 4