What dose of amoxicillin suspension (400 mg/5 mL) should be given to a 36‑pound (≈16.3 kg) child?

Amoxicillin 400mg/5mL Dosing for a 36-Pound Child

For a 36-pound (16.3 kg) child, administer 6 mL of amoxicillin 400mg/5mL suspension twice daily for standard-dose indications, or 12 mL twice daily for high-dose indications.

Weight-Based Calculation

• The child weighs 36 pounds = 16.3 kg 1
• Standard-dose regimen (45 mg/kg/day): 16.3 kg × 45 mg/kg/day = 734 mg/day, divided into 2 doses = 367 mg per dose 1, 2
• Using the 400mg/5mL suspension: 367 mg ÷ 80 mg/mL = 4.6 mL per dose, rounded to 5–6 mL twice daily 1
• High-dose regimen (90 mg/kg/day): 16.3 kg × 90 mg/kg/day = 1,467 mg/day, divided into 2 doses = 734 mg per dose 1, 3
• Using the 400mg/5mL suspension: 734 mg ÷ 80 mg/mL = 9.2 mL per dose, rounded to 9–10 mL twice daily (or conservatively 12 mL to ensure adequate dosing) 1, 3

Indication-Based Dosing Algorithm

Standard-Dose Indications (45 mg/kg/day = ~6 mL twice daily)

• Uncomplicated respiratory tract infections in children ≥2 years without recent antibiotic exposure 1, 2
• Acute bacterial sinusitis in children ≥2 years who do not attend daycare and have not received antibiotics in the past 4 weeks 1
• Mild-to-moderate skin infections or genitourinary infections 2
• Group A streptococcal pharyngitis at 50–75 mg/kg/day (8–12 mL twice daily for this indication) 1

High-Dose Indications (90 mg/kg/day = ~12 mL twice daily)

• Community-acquired pneumonia (presumed bacterial) in all children to cover penicillin-resistant Streptococcus pneumoniae 1, 3
• Severe respiratory tract infections or lower respiratory tract infections 1, 2
• Any of the following risk factors:
  • Age < 2 years 1
  • Daycare attendance 1
  • Recent antibiotic use (within past 30 days) 1
  • Residence in an area with > 10% penicillin-resistant S. pneumoniae 1
  • Moderate-to-severe illness 1
• Acute bacterial sinusitis in children < 2 years, daycare attendees, or those with recent antibiotic exposure 1

Treatment Duration

• Respiratory infections (pneumonia, sinusitis): Continue for 7–10 days, with pneumonia specifically requiring 10 days 1
• Group A streptococcal pharyngitis: Complete a full 10-day course to prevent acute rheumatic fever 1, 2
• General principle: Continue therapy for a minimum of 48–72 hours beyond symptom resolution 1, 2

Critical Dosing Considerations

• Maximum daily dose: The absolute maximum is 4,000 mg/day regardless of weight 1, 4
• Twice-daily dosing is preferred over three-times-daily dosing because it improves adherence and achieves superior pharmacokinetic profiles 3, 5, 6
• Administer at the start of a meal to minimize gastrointestinal intolerance 2
• Shake the suspension well before each use and discard any unused portion after 14 days 2

When to Switch to Amoxicillin-Clavulanate

• Suspected β-lactamase-producing organisms (Haemophilus influenzae, Moraxella catarrhalis) warrant escalation to amoxicillin-clavulanate 90 mg/kg/day (amoxicillin component) in 2 doses 1, 7, 8
• Treatment failure after 48–72 hours on amoxicillin alone 1
• Incomplete H. influenzae type b vaccination or concurrent purulent acute otitis media 1

Monitoring and Follow-Up

• Clinical improvement should occur within 48–72 hours; if no improvement, reevaluate and consider atypical pathogens or resistant organisms 1, 3
• Fever typically resolves within 24–48 hours for pneumococcal infections, though cough may persist longer 1
• Complete the full prescribed course even if symptoms improve before completion 1, 2

Common Pitfalls to Avoid

• Do not underdose: For pneumonia or severe infections, the high-dose regimen (90 mg/kg/day) is essential to overcome resistant S. pneumoniae 1, 3
• Do not use age-based dosing: Always calculate based on weight in kilograms 1, 9
• Do not stop antibiotics early: Premature discontinuation increases resistance and recurrence risk 1, 2
• Do not exceed maximum daily dose: Even with high-dose regimens, never exceed 4,000 mg/day total 1, 4