What is the appropriate amoxicillin dose for a 47.2‑lb (21.4‑kg) child using a suspension concentration of 400 mg per 5 mL?

Amoxicillin Dose Calculation for a 47.2 lb Child Using 400mg/5mL Suspension

For a 47.2 lb (21.4 kg) child, the appropriate amoxicillin dose depends on the indication: for mild to moderate respiratory infections, administer 5.4 mL of 400mg/5mL suspension twice daily (approximately 45 mg/kg/day); for severe infections or high-resistance areas, administer 10.7 mL twice daily (approximately 90 mg/kg/day). 1

Weight-Based Dosing Algorithm

Step 1: Convert Weight and Calculate Daily Dose

• The child weighs 47.2 lbs, which equals 21.4 kg 1
• For mild to moderate infections: 45 mg/kg/day = 21.4 kg × 45 mg/kg = 963 mg/day, divided into 2 doses = 481.5 mg per dose 1
• For severe infections or high pneumococcal resistance: 90 mg/kg/day = 21.4 kg × 90 mg/kg = 1,926 mg/day, divided into 2 doses = 963 mg per dose 1

Step 2: Convert to Volume Using 400mg/5mL Concentration

• Mild to moderate infections: 481.5 mg ÷ 400 mg × 5 mL = 6.0 mL twice daily 1
• Severe infections: 963 mg ÷ 400 mg × 5 mL = 12.0 mL twice daily 1

Indication-Specific Dosing

Community-Acquired Pneumonia (Mild to Moderate)

• Standard dose: 45 mg/kg/day divided every 12 hours = approximately 6 mL of 400mg/5mL suspension twice daily 1
• This provides adequate coverage for most susceptible pathogens including Streptococcus pneumoniae, Haemophilus influenzae (non-β-lactamase producing), and Streptococcus pyogenes 1

Severe Infections or High-Resistance Areas

• High-dose regimen: 90 mg/kg/day divided every 12 hours = approximately 12 mL of 400mg/5mL suspension twice daily 1
• This dosing is indicated for areas with >10% penicillin-resistant S. pneumoniae, children <2 years old, recent antibiotic exposure within 30 days, daycare attendance, or severe infections requiring hospitalization 1

Group A Streptococcal Pharyngitis

• Recommended dose: 50-75 mg/kg/day divided into 2 doses for 10 days 1
• For this 21.4 kg child: 1,070-1,605 mg/day = 535-802 mg per dose = approximately 6.7-10 mL twice daily 1
• Maximum single dose should not exceed 1,000 mg 1

Treatment Duration and Monitoring

• Standard duration: 7-10 days for most respiratory infections; pneumonia specifically requires 10 days 1
• Streptococcal infections: Minimum 10 days to prevent acute rheumatic fever 2, 3
• Clinical improvement expected within 48-72 hours; if no improvement occurs, reevaluation and further investigation are necessary 1

Critical Dosing Considerations

• Maximum daily dose: Should not exceed 4,000 mg/day regardless of weight 1
• For β-lactamase-producing organisms (H. influenzae, M. catarrhalis): Use amoxicillin-clavulanate (Augmentin) at 90 mg/kg/day of the amoxicillin component instead of amoxicillin alone 1, 4
• Administration: Should be taken at the start of a meal to minimize gastrointestinal intolerance 3

Common Pitfalls to Avoid

• Do not underdose: Using 45 mg/kg/day when 90 mg/kg/day is indicated (severe infection, high resistance) leads to treatment failure with resistant organisms 1
• Do not use amoxicillin alone for β-lactamase producers: Switch to amoxicillin-clavulanate if H. influenzae or M. catarrhalis is suspected 1, 4
• Verify suspension concentration before dispensing: The 400mg/5mL concentration is different from standard 250mg/5mL or 125mg/5mL formulations 3
• Shake suspension well before each use and discard any unused portion after 14 days 3