Cephalexin Dosing for an 8-Year-Old Child Weighing 26.9 kg
For this 26.9 kg child, administer cephalexin 675 mg every 6 hours (four times daily) for most infections, or 1,350 mg every 12 hours (twice daily) for streptococcal pharyngitis, skin infections, or uncomplicated urinary tract infections. 1
Standard Dosing Calculation
The FDA-approved dosing for pediatric patients is 25 to 50 mg/kg/day in divided doses 1:
Standard dose (25 mg/kg/day): 26.9 kg × 25 mg/kg = 672.5 mg/day
- Divided every 6 hours (QID): ~170 mg per dose (675 mg/day total)
- Divided every 12 hours (BID): ~335 mg per dose (670 mg/day total)
Higher dose (50 mg/kg/day): 26.9 kg × 50 mg/kg = 1,345 mg/day
- Divided every 6 hours (QID): ~335 mg per dose (1,340 mg/day total)
- Divided every 12 hours (BID): ~675 mg per dose (1,350 mg/day total)
Infection-Specific Recommendations
For Streptococcal Pharyngitis or Skin/Soft Tissue Infections
The total daily dose may be divided and administered every 12 hours for these specific infections 1. For this 26.9 kg child, use 335-675 mg twice daily depending on infection severity 1.
For Otitis Media
Clinical studies demonstrate that 75 to 100 mg/kg/day in 4 divided doses is required 1. For this child:
- 75 mg/kg/day = 2,017.5 mg/day ÷ 4 = ~505 mg every 6 hours
- 100 mg/kg/day = 2,690 mg/day ÷ 4 = ~670 mg every 6 hours
For Methicillin-Susceptible Staphylococcus aureus (MSSA) Infections
Cephalexin is the preferred oral agent for MSSA infections per the American Academy of Pediatrics and Infectious Diseases Society of America 2, 3. The recommended dose is 75-100 mg/kg/day in 3 or 4 doses 2:
- For this 26.9 kg child: 505-670 mg every 6 hours (four times daily)
- Alternative twice-daily dosing: Recent evidence suggests 22-45 mg/kg per dose twice daily may be adequate for MSSA with MIC ≤2 mg/L 4, which would be 590-1,210 mg twice daily for this child
For Severe Infections
The dosage may be doubled 1. This would mean up to 100 mg/kg/day (2,690 mg/day for this child), divided into appropriate intervals.
Practical Dosing Using Available Formulations
Using the 250 mg/5 mL suspension 1:
- Standard dosing (25 mg/kg/day QID): 3.5 mL (175 mg) every 6 hours
- Higher dosing (50 mg/kg/day QID): 7 mL (350 mg) every 6 hours
- Twice-daily dosing: 13.5 mL (675 mg) every 12 hours
Alternatively, 250 mg or 500 mg capsules can be used for older children who can swallow pills 1.
Important Clinical Considerations
Duration of Therapy
- For β-hemolytic streptococcal infections, administer for at least 10 days 1
- For cystitis, continue therapy for 7 to 14 days 1, 5
Limitations
Cephalexin has poor activity against Haemophilus influenzae, with failure rates of approximately 50% in H. influenzae otitis media 6, 7. Consider alternative antibiotics if H. influenzae is suspected or confirmed 6.
Storage
After mixing the suspension, store in refrigerator and discard after 14 days 1.
Dosing Frequency and Adherence
While four-times-daily dosing is traditionally recommended, twice-daily dosing improves medication compliance and is FDA-approved for specific infections including streptococcal pharyngitis and skin infections 1, 4, 8. Recent pharmacokinetic modeling supports less frequent dosing regimens for MSSA infections 4.