What is the recommended dose of cefalexin (cephalexin) for pediatric patients with varying weights and potential impaired renal function?

Cefalexin Dosing for Pediatric Patients

Standard Dosing Recommendations

For most pediatric infections in children over 1 month of age, cefalexin should be dosed at 25-100 mg/kg/day divided into 2-4 doses depending on infection severity, with typical dosing being 25-50 mg/kg/day for mild infections and up to 100 mg/kg/day for severe infections. 1

Infection-Specific Dosing

For methicillin-susceptible Staphylococcus aureus (MSSA) infections:

• Oral therapy (step-down or mild infection): 75-100 mg/kg/day divided into 3 or 4 doses 2
• This provides optimal coverage for MSSA pneumonia and other serious staphylococcal infections 2

For bone and joint infections:

• High-dose regimen: 45 mg/kg/dose (maximum 1.5 g) three times daily is effective and well-tolerated 3
• This reduced-frequency regimen achieved 99% cure rates in a recent study of 149 children 3
• Improves adherence compared to traditional four-times-daily dosing 3

For urinary tract infections in infants 29-60 days old:

• 50-100 mg/kg/day divided into 4 doses 2
• Alternative oral option when transitioning from parenteral therapy 2

Age-Specific Considerations

For infants 7-60 days old:

• 25 mg/kg/dose every 6 hours achieves >90% target attainment for Enterobacterales (MIC ≤2 mg/L) 4
• 25 mg/kg/dose every 8 hours is sufficient for MSSA (MIC ≤2 mg/L) 4
• Maturational changes in absorption and renal clearance affect dosing in this age group 4

For children 1-16 years:

• Twice-daily dosing: 22-45 mg/kg/dose for MSSA with MIC 1-2 mg/L; 80 mg/kg/dose for MIC 4 mg/L 5
• Three-times-daily dosing: 15-25 mg/kg/dose for MSSA with MIC 1-2 mg/L; 45 mg/kg/dose for MIC 4 mg/L 5

Dosing Algorithm by Clinical Scenario

Mild to Moderate Infections (e.g., uncomplicated skin infections)

• 25-50 mg/kg/day divided into 2-4 doses 1
• For a 9 kg child: approximately 75 mg every 8 hours 1

Severe Infections (e.g., MSSA pneumonia, osteomyelitis)

• 75-100 mg/kg/day divided into 3-4 doses 2
• Alternative: 45 mg/kg/dose (maximum 1.5 g) three times daily for bone and joint infections 3

Step-Down Therapy from IV Antibiotics

• 75-100 mg/kg/day divided into 3-4 doses for MSSA infections 2
• Ensure clinical improvement before transitioning to oral therapy 2

Renal Function Considerations

While the provided guidelines do not specify dose adjustments for impaired renal function in pediatric patients, cefalexin is renally eliminated and requires adjustment in adults with renal impairment. For pediatric patients with known or suspected renal dysfunction, consult nephrology or use alternative agents with better-established pediatric dosing in renal impairment. 1

Critical Clinical Considerations

Cefalexin is inadequate for serious infections requiring broader coverage (e.g., not fully immunized children, suspected resistant organisms), and alternative agents like amoxicillin-clavulanate or cefazolin should be used instead 1

Common tolerability issues:

• Gastrointestinal symptoms occur in approximately 3% of children on high-dose regimens 3
• Mild neutropenia may develop in approximately 9% of children, typically without clinical complications 3

Cefalexin is NOT appropriate for:

• Pneumococcal pneumonia (amoxicillin 90 mg/kg/day is first-line) 2
• Infections requiring coverage for β-lactamase-producing organisms 2
• Methicillin-resistant Staphylococcus aureus (MRSA) 2