What is the recommended dose of cefalexin (cephalexin) for infants with uncomplicated infections, considering their weight and potential impaired renal function?

Cefalexin Dosing for Infants

For infants, cefalexin is dosed at 25-50 mg/kg/day divided into 2-4 doses depending on infection severity, with the FDA-approved standard being 25-50 mg/kg/day in divided doses for most infections. 1

Standard Dosing by Age and Indication

Infants 29-60 Days Old

• For urinary tract infections: 50-100 mg/kg/day divided into 4 doses (every 6 hours) 2, 3
• This dosing is recommended when transitioning from parenteral therapy in well-appearing febrile infants 2

General Pediatric Dosing (>1 month)

• Mild to moderate infections: 25-50 mg/kg/day divided into 2-4 doses 1
• Severe infections: Up to 100 mg/kg/day in divided doses 1
• Otitis media: 75-100 mg/kg/day in 4 divided doses 1

Infection-Specific Recommendations

Methicillin-Susceptible Staphylococcus aureus (MSSA)

• 75-100 mg/kg/day divided into 3-4 doses for MSSA skin and soft tissue infections or bone/joint infections 3, 4
• Recent evidence supports 45 mg/kg/dose (maximum 1.5 g) three times daily as an effective alternative with improved adherence 4

Streptococcal Pharyngitis and Skin Infections

• Total daily dose may be divided and administered every 12 hours in patients over 1 year of age 1
• Treatment duration should be at least 10 days for β-hemolytic streptococcal infections 1

Critical Considerations for Renal Impairment

Dosage adjustment is essential in infants with impaired renal function, as cefalexin is primarily renally eliminated 1. The FDA label does not provide specific pediatric renal dosing adjustments, but close monitoring and dose reduction based on creatinine clearance is necessary 1.

Important Limitations

• Cefalexin is NOT appropriate for:
  • Pneumococcal pneumonia (use amoxicillin 90 mg/kg/day instead) 3
  • β-lactamase-producing organisms 3
  • Methicillin-resistant Staphylococcus aureus (MRSA) 3
  • Serious infections requiring broader coverage (consider amoxicillin-clavulanate or cefazolin) 3

Practical Administration

• Suspension preparation: Available as 125 mg/5 mL or 250 mg/5 mL suspensions 1
• Storage: After mixing, refrigerate and use within 14 days 1
• Dosing frequency: Four times daily dosing is standard, though twice or three times daily regimens show promise for improving adherence in older children 4, 5

Emerging Evidence for Young Infants

Recent pharmacokinetic modeling in infants 7-60 days old suggests 25 mg/kg/dose every 6-8 hours achieves appropriate pharmacodynamic targets for Enterobacterales and MSSA 6. For Enterobacterales, every 6 hours dosing is preferred; for MSSA, every 8 hours may be sufficient 6.