What is the appropriate pediatric amoxicillin dose for a child weighing 50 lb using a suspension that contains 400 mg per 5 mL?

Amoxicillin Dosing for a 50-Pound Child Using 400mg/5mL Suspension

For a child weighing 50 pounds (22.7 kg), administer 11.4 mL of the 400mg/5mL suspension twice daily (total daily dose of approximately 80 mg/kg/day) for most common bacterial infections requiring high-dose amoxicillin therapy.

Weight Conversion and Dose Calculation

• Weight conversion: 50 pounds = 22.7 kg
• Standard high-dose amoxicillin: 80-90 mg/kg/day divided into 2 doses 1
• Calculated total daily dose: 22.7 kg × 80 mg/kg = 1,816 mg/day
• Per-dose amount: 1,816 mg ÷ 2 = 908 mg per dose
• Volume per dose: 908 mg ÷ (400 mg/5 mL) = 11.4 mL twice daily

Clinical Context for Dosing

High-Dose Amoxicillin Indications (80-90 mg/kg/day)

Use this higher dose for:

• Streptococcus pneumoniae infections with penicillin MICs >2.0 μg/mL, including community-acquired pneumonia 1
• Acute otitis media in areas with resistant pneumococcal strains 2, 3
• Group A Streptococcus infections requiring 50-75 mg/kg/day 1

Standard-Dose Amoxicillin (40-50 mg/kg/day)

Use lower doses for:

• Uncomplicated acute otitis media in low-resistance areas: 40 mg/kg/day 4, 5
• Haemophilus influenzae (β-lactamase negative): 75-100 mg/kg/day in 3 doses 1

Practical Dosing Considerations

Maximum Dose Concerns

• Adult maximum dose: Standard adult amoxicillin dosing is 1,500 mg/day for routine infections 2
• This child's calculated dose (1,816 mg/day) exceeds the standard adult dose, which is appropriate for high-dose therapy 6, 2
• Do not artificially cap at adult doses when treating resistant pneumococcal infections requiring 80-90 mg/kg/day 1, 6

Dosing Frequency

• Twice-daily dosing (every 12 hours) is preferred for high-dose regimens (90 mg/kg/day in 2 doses) 1
• Three-times-daily dosing (every 8 hours) can be used (45 mg/kg/day in 3 doses) 1
• For this child: 11.4 mL twice daily is simpler and equally effective 1

Common Pitfalls to Avoid

Weight-Based Dosing Disparities

• Larger children frequently receive inadequate doses when clinicians inappropriately cap at "adult maximum" doses 6
• Children >60 kg often receive <40 mg/kg/day when they should receive 80-90 mg/kg/day for resistant infections 6
• Small children may receive excessive doses while larger children are underdosed due to arbitrary adult dose limits 6

Duration of Therapy

• Standard duration: 5-7 days for most infections 5, 7, 8
• 3-day courses may be adequate for uncomplicated pneumonia but show slightly longer cough duration (12 vs 10 days) 7, 8
• 7-day courses remain standard for acute otitis media and pneumonia 7, 8

Alternative Formulations

If the 400mg/5mL suspension is unavailable:

• 250mg/5mL suspension: Would require 18.2 mL twice daily (less practical)
• Tablets: 875 mg tablet + 125 mg (1.6 mL of 400mg/5mL) twice daily if child can swallow tablets 9

Monitoring and Follow-Up

• Reassess at 48-72 hours if symptoms worsen or fail to improve 7, 8
• Antibiotic re-treatment rate: Approximately 12-13% within 28 days regardless of dose (35-50 mg/kg vs 70-90 mg/kg) 8
• Common adverse effects: Diarrhea, rash, thrush—similar rates across dosing regimens 7, 8