What dose of cephalexin (250 mg per 5 mL suspension) should be given to a child weighing 30 lb?

Cephalexin Dosing for 30-Pound Child

For a 30-pound (13.6 kg) child, give 3.4 mL of cephalexin 250 mg/5 mL suspension every 6 hours (four times daily), or 6.8 mL every 12 hours (twice daily) for most infections.

Dosing Calculation

The child weighs 30 pounds, which equals approximately 13.6 kg.

Standard Dosing Regimen

According to the FDA-approved dosing, the usual pediatric dose is 25 to 50 mg/kg/day divided into doses 1. For most common infections:

• Lower end (25 mg/kg/day): 13.6 kg × 25 mg/kg = 340 mg/day

  • Divided every 6 hours (QID): 85 mg per dose = 1.7 mL per dose
  • Divided every 12 hours (BID): 170 mg per dose = 3.4 mL per dose

• Standard dose (40 mg/kg/day): 13.6 kg × 40 mg/kg = 544 mg/day

  • Divided every 6 hours (QID): 136 mg per dose = 2.7 mL per dose
  • Divided every 12 hours (BID): 272 mg per dose = 5.4 mL per dose

• Higher end (50 mg/kg/day): 13.6 kg × 50 mg/kg = 680 mg/day

  • Divided every 6 hours (QID): 170 mg per dose = 3.4 mL per dose
  • Divided every 12 hours (BID): 340 mg per dose = 6.8 mL per dose

Practical Dosing Recommendations

For most infections (skin/soft tissue, streptococcal pharyngitis):

• Use 50 mg/kg/day dosing
• Four times daily: 3.4 mL (170 mg) every 6 hours
• Twice daily alternative: 6.8 mL (340 mg) every 12 hours 1

The FDA label specifically states that for streptococcal pharyngitis and skin/soft tissue infections in pediatric patients over 1 year of age, the total daily dose may be divided and administered every 12 hours 1.

Indication-Specific Adjustments

For otitis media (more severe):

• Use 75-100 mg/kg/day in 4 divided doses 1
• This would be 1020-1360 mg/day (255-340 mg per dose)
• Dose: 5.1-6.8 mL every 6 hours

For methicillin-susceptible Staphylococcus aureus infections:

• Guidelines recommend 75-100 mg/kg/day in 3-4 divided doses 2
• Dose: 5.1-6.8 mL every 6-8 hours

Important Clinical Considerations

Dosing Frequency Options

Recent pharmacokinetic studies support less frequent dosing to improve adherence 3, 4:

• Twice daily dosing is effective for most infections and improves compliance
• Three times daily dosing at 45 mg/kg/dose (maximum 1.5 g) has shown excellent efficacy for bone/joint infections 5
• Four times daily remains the traditional FDA-approved regimen but has adherence challenges

Common Pitfalls

1. Weight-based dosing errors: Patients over 20 kg are at highest risk for overdosing when prescribers use maximum adult doses inappropriately 6
2. Underdosing: For this 30-pound child, ensure at least 25 mg/kg/day; many infections require 40-50 mg/kg/day
3. Duration: For streptococcal infections, treat for at least 10 days 1

Storage and Preparation

After mixing the suspension, refrigerate and discard after 14 days 1. Shake well before each use.