Cephalexin Liquid Dosing for a 19.8-kg Child
For a 19.8-kg child, give cephalexin oral suspension 500 mg (10 mL of 250 mg/5 mL suspension) every 6 hours, or 500 mg every 8 hours for most infections.
Dosing Calculation
The standard pediatric dosing for cephalexin is 25-50 mg/kg/day divided into multiple doses 1. For this 19.8-kg child:
- Standard dosing (25-50 mg/kg/day): 495-990 mg/day total
- Divided every 6 hours (QID): 125-250 mg per dose
- Divided every 8 hours (TID): 165-330 mg per dose
However, practical dosing using available suspension strengths (125 mg/5 mL or 250 mg/5 mL) 1:
For Most Infections (Skin/Soft Tissue, Pharyngitis)
- 500 mg (10 mL of 250 mg/5 mL) every 6 hours achieves approximately 100 mg/kg/day
- OR 500 mg every 8 hours for less severe infections (approximately 75 mg/kg/day)
For Severe Infections or Resistant Organisms
- Dosing may be doubled to 100 mg/kg/day 1
- This would be 500 mg every 6 hours (approximately 100 mg/kg/day)
Context-Specific Recommendations
For methicillin-susceptible Staphylococcus aureus (MSSA) infections (bone/joint, complicated skin infections):
- The preferred oral dose is 75-100 mg/kg/day divided into 3-4 doses 2, 3
- For this child: 500 mg every 6-8 hours (approximately 75-100 mg/kg/day)
For otitis media specifically:
- 75-100 mg/kg/day in 4 divided doses is required 1
- For this child: 375-500 mg every 6 hours
For streptococcal pharyngitis or uncomplicated skin infections:
- May use every 12-hour dosing 1
- For this child: 500 mg twice daily is acceptable
Practical Suspension Preparation
Using the 250 mg/5 mL suspension 1:
- Each 5 mL (1 teaspoon) = 250 mg
- Give 10 mL (2 teaspoons) per dose for 500 mg
- Store in refrigerator after mixing
- Discard after 14 days
Important Caveats
Recent pharmacokinetic data supports less frequent dosing: 45 mg/kg three times daily (maximum 1.5 g/dose) achieves adequate drug levels and improves adherence 4, 5
For this 19.8-kg child using the newer regimen: 890 mg (approximately 900 mg) three times daily would be appropriate, though this exceeds typical suspension volumes
Duration: Most infections require 7-10 days of therapy 1
Streptococcal infections: Must treat for at least 10 days 1
The standard four-times-daily dosing is often challenging for adherence; three-times-daily dosing at higher individual doses (45 mg/kg/dose, max 1.5 g) has been shown effective and well-tolerated 4, 5
The most practical approach for this 19.8-kg child is 500 mg (10 mL of 250 mg/5 mL suspension) every 6-8 hours, depending on infection severity and type.