What is the recommended dosage of cephalexin (a cephalosporin antibiotic) for a 13kg child?

Cephalexin Dosing for a 13kg Child

For a 13kg child, administer cephalexin 325-650 mg per day divided into 2-4 doses, which translates to 3.25-6.5 mL of the 100mg/mL suspension per dose depending on infection severity and dosing frequency. 1

Standard Dosing Algorithm

Weight-Based Calculation:

• The FDA-approved pediatric dosage for cephalexin is 25-50 mg/kg/day in divided doses 1
• For a 13kg child:
  • Standard dose: 25 mg/kg/day = 325 mg/day total
  • Higher dose: 50 mg/kg/day = 650 mg/day total 1

Dosing Frequency Options

Four Times Daily (Q.I.D.) Regimen:

• Standard infections: 1.6-3.25 mL (80-160 mg) every 6 hours 1
• This provides 325-650 mg/day total 1

Twice Daily (B.I.D.) Regimen:

• For streptococcal pharyngitis and skin/skin structure infections: 3.25-6.5 mL (162.5-325 mg) every 12 hours 1
• Recent pharmacokinetic studies support twice-daily dosing of 22-45 mg/kg/dose for methicillin-susceptible Staphylococcus aureus infections with MIC ≤2 mg/L 2

Three Times Daily (T.I.D.) Regimen:

• High-dose regimen: 45 mg/kg/dose (maximum 1.5g) three times daily has demonstrated 99% cure rates for bone and joint infections 3
• For a 13kg child: approximately 6 mL (585 mg) three times daily for severe infections 3

Indication-Specific Dosing

Severe Infections or Otitis Media:

• The FDA label specifies 75-100 mg/kg/day in 4 divided doses for otitis media 1
• For a 13kg child: 975-1300 mg/day = 4.9-6.5 mL every 6 hours 1
• Dosage may be doubled for severe infections 1

Streptococcal Infections:

• Continue therapeutic dosage for at least 10 days for β-hemolytic streptococcal infections 1

Critical Considerations

Pharmacokinetic Rationale:

• Children require higher doses per kilogram than adults due to greater body water turnover 4
• Cephalexin achieves urinary concentrations of 500-1000 mcg/mL following 250-500 mg doses, far exceeding MIC for common urinary pathogens 4
• The drug is rapidly absorbed in the upper intestine and does not disturb lower bowel flora 4

Common Pitfalls:

• Less frequent dosing (BID or TID) improves adherence but requires higher individual doses 2
• Gastrointestinal symptoms occur in <3% of children on high-dose regimens 3
• Mild neutropenia may develop in approximately 9% of children on prolonged therapy but is typically asymptomatic 3

Storage and Preparation:

• After reconstitution, refrigerate and use within 14 days 1