What is the appropriate amoxicillin (400 mg/5 mL) dosage for a 56‑lb (≈25 kg) child with streptococcal pharyngitis and acute otitis media?

Amoxicillin Dosing for Strep Pharyngitis and Ear Infection in a 56-lb Child

For a 56-lb (25 kg) child with both streptococcal pharyngitis and acute otitis media, prescribe amoxicillin 400 mg/5 mL suspension at 10 mL (800 mg) twice daily for 10 days.

Dosing Calculation and Rationale

A 56-lb child weighs approximately 25 kg. For concurrent strep throat and ear infection, you need to use the higher dosing regimen since acute otitis media requires more aggressive treatment than strep pharyngitis alone.

For Acute Otitis Media (the higher dose requirement):

• FDA-approved dosing: 45 mg/kg/day divided every 12 hours for severe ear/nose/throat infections 1
• Calculation: 25 kg × 45 mg/kg/day = 1,125 mg/day
• Divided twice daily: ~560 mg per dose
• Practical dosing with 400 mg/5 mL suspension: 7 mL (560 mg) twice daily

However, current guidelines recommend even higher dosing (80-90 mg/kg/day) for AOM to combat drug-resistant Streptococcus pneumoniae 2. This translates to:

• 25 kg × 80 mg/kg/day = 2,000 mg/day
• Divided twice daily: 1,000 mg per dose = 12.5 mL twice daily

For Streptococcal Pharyngitis:

• The IDSA guideline recommends 50 mg/kg once daily (max 1000 mg) OR 25 mg/kg twice daily (max 500 mg per dose) 3
• For this child: 25 kg × 25 mg/kg = 625 mg per dose twice daily

Practical Recommendation

The most practical and evidence-based approach is 10 mL (800 mg) twice daily, which provides:

• 1,600 mg/day total (64 mg/kg/day)
• This exceeds the FDA minimum for severe infections (45 mg/kg/day) 1
• Approaches the AAP-recommended high-dose for AOM (80-90 mg/kg/day) 2
• Far exceeds strep pharyngitis requirements (50 mg/kg/day) 3

If you want to be more aggressive (especially if the child attends daycare or had recent antibiotics), prescribe 12.5 mL (1000 mg) twice daily to reach the full 80 mg/kg/day target.

Duration and Key Points

• Duration: 10 days for both conditions 3, 1

  • Strep pharyngitis requires at least 10 days to prevent acute rheumatic fever 3, 1
  • AOM typically treated for 10 days in young children 2

• Administration: Give at the start of meals to minimize GI upset 1

• Follow-up: Reassess if symptoms worsen or fail to improve within 48-72 hours 2

Common Pitfalls to Avoid

• Don't underdose: Standard dosing (40-45 mg/kg/day) is inadequate for AOM in the era of resistant pneumococcus 2, 4, 5
• Don't use amoxicillin-clavulanate as first-line unless the child received amoxicillin in the past 30 days or has concurrent purulent conjunctivitis 2
• Don't shorten the course for strep pharyngitis—10 days is required to prevent rheumatic fever 3, 1
• Shake the suspension well before each dose and discard after 14 days 1