Cephalexin Dosing for a 6.6 kg Child
For a child weighing 6.6 kg, the appropriate cephalexin dose using the 125 mg/5 mL suspension is 2.5 mL (62.5 mg) given 3-4 times daily, or 3.3 mL (82.5 mg) given 3-4 times daily for more severe infections.
Dosing Calculation
The FDA-approved pediatric dosing for cephalexin is 25-50 mg/kg/day divided into 3-4 doses 1. For this 6.6 kg child:
Standard dosing (25 mg/kg/day): 165 mg/day total
- Divided QID (4 times daily): 41.25 mg per dose = 2 mL per dose
- Divided TID (3 times daily): 55 mg per dose = 2.2 mL per dose
Higher dosing (50 mg/kg/day): 330 mg/day total
- Divided QID: 82.5 mg per dose = 3.3 mL per dose
- Divided TID: 110 mg per dose = 4.4 mL per dose
Practical Dosing Recommendations
For most common infections (skin/soft tissue, streptococcal pharyngitis):
- Give 2.5 mL (62.5 mg) four times daily using the 125 mg/5 mL suspension
- This provides approximately 38 mg/kg/day, which falls within the recommended range
For more severe infections or less susceptible organisms:
- Give 3.5 mL (87.5 mg) four times daily
- This provides approximately 53 mg/kg/day
For improved adherence with twice-daily dosing:
- Recent pharmacokinetic studies support less frequent dosing 2
- Give 5 mL (125 mg) twice daily for standard infections
- This provides approximately 38 mg/kg/day with better compliance
Context-Specific Guidance
The indication matters significantly for cephalexin dosing:
For methicillin-susceptible Staphylococcus aureus infections, guidelines recommend 75-100 mg/kg/day divided into 3-4 doses 3, 4. For this 6.6 kg child, this would be:
- 495-660 mg/day total
- 5 mL (125 mg) QID would provide 76 mg/kg/day (appropriate)
For otitis media, the FDA label specifies that 75-100 mg/kg/day in 4 divided doses is required 1:
- Give 5 mL (125 mg) four times daily
- This provides 76 mg/kg/day
Important Caveats
- The FDA dosing table in the label lists a 10 kg child as the lowest weight, recommending 1/2 to 1 teaspoon (2.5-5 mL) QID of the 125 mg/5 mL suspension 1
- For a 6.6 kg child, proportional reduction suggests starting at the lower end of this range
- Severe infections may require doubling the dose per FDA guidance 1
- Maximum daily dose should not exceed 4 grams, though this is not a concern at this weight
- Recent evidence supports high-dose TID dosing (45 mg/kg/dose, maximum 1.5 g) for bone and joint infections with excellent efficacy and tolerability 5, though this exceeds traditional recommendations
Dosing Frequency Considerations
While QID dosing is traditional, TID or BID dosing improves adherence without compromising efficacy for most infections 2. For this child:
- TID dosing: 3.5 mL (87.5 mg) three times daily provides 40 mg/kg/day
- BID dosing: 5 mL (125 mg) twice daily provides 38 mg/kg/day
These reduced-frequency regimens are particularly valuable for outpatient treatment where medication burden affects compliance.