FDA Approval Status for Cephalexin in Infants Under 12 Months
Yes, oral cephalexin (Keflex) is FDA-approved for use in pediatric patients, including infants under 12 months of age, and can be used to treat cellulitis in an 8-month-old infant.
FDA Label Evidence
The FDA drug label for Keflex explicitly addresses pediatric use: "The safety and effectiveness of Keflex in pediatric patients was established in clinical trials for the dosages described in the DOSAGE AND ADMINISTRATION section" 1. Importantly, the label does not specify any lower age limit for use, and the pediatric dosing recommendations apply broadly to children capable of receiving the medication 1.
Dosing for Infants
According to the IDSA guidelines, the standard pediatric dose for cephalexin in skin and soft tissue infections is 25-50 mg/kg/day divided into 3-4 doses 2. For an 8-month-old infant with cellulitis:
- Standard dosing: 25-50 mg/kg/day in 3-4 divided doses orally
- This translates to approximately 25 mg/kg/dose every 6-8 hours
Recent Pharmacokinetic Data Supporting Use in Young Infants
A 2025 pharmacokinetic study specifically evaluated cephalexin in infants as young as 7-60 days old and demonstrated that 25 mg/kg/dose every 6-8 hours achieves appropriate pharmacodynamic targets for common pathogens causing cellulitis, including methicillin-susceptible Staphylococcus aureus (MSSA) and Enterobacterales 3. This study found:
- For MSSA: 25 mg/kg/dose every 8 hours was sufficient
- For Enterobacterales: 25 mg/kg/dose every 6 hours achieved >90% target attainment
Clinical Effectiveness in Young Children
A 2022 retrospective study of high-dose oral cephalexin for moderate cellulitis in children demonstrated an 89.7% success rate with excellent safety profile 4. While this study included older children, it supports the efficacy and safety of cephalexin for cellulitis in the pediatric population.
Important Caveats
- Renal function monitoring: The FDA label notes that cephalexin is substantially excreted by the kidney, so careful monitoring is warranted in any patient with impaired renal function 1
- Capsule formulation: Keflex capsules should only be used in children capable of swallowing them; oral suspension is the appropriate formulation for an 8-month-old 1
- Pathogen coverage: Cephalexin provides excellent coverage for streptococci and MSSA but does not cover MRSA 2. If MRSA is suspected (purulent infection, local resistance patterns, treatment failure), alternative agents are needed
Bottom Line
Oral cephalexin is FDA-approved without age restriction for pediatric use, including infants under 12 months. For an 8-month-old with cellulitis, use the oral suspension at 25-50 mg/kg/day divided every 6-8 hours, targeting streptococcal and MSSA pathogens 2, 1, 3.