What is the appropriate amoxicillin dose for a 5‑year‑old child weighing 16.8 kg using a suspension of 400 mg per 5 mL?

Amoxicillin Dosing for a 5-Year-Old Weighing 16.78 kg

For this child, prescribe amoxicillin 375 mg (approximately 3.75 mL of the 400 mg/5 mL suspension) twice daily, which delivers 45 mg/kg/day for mild to moderate respiratory tract infections, or 750 mg (7.5 mL) twice daily for severe infections or high pneumococcal resistance areas, delivering 90 mg/kg/day. 1

Dosing Algorithm Based on Clinical Indication

For Mild to Moderate Respiratory Infections

• The standard dose is 45 mg/kg/day divided into 2 doses (every 12 hours). 1, 2
• For a 16.78 kg child: 16.78 kg × 45 mg/kg/day = 755 mg/day total, which equals 377.5 mg per dose (approximately 3.75 mL twice daily using 400 mg/5 mL suspension). 1
• This regimen provides adequate coverage for Streptococcus pneumoniae, non-β-lactamase-producing Haemophilus influenzae, and Streptococcus pyogenes. 1

For Severe Infections or High Pneumococcal Resistance

• Use the high-dose regimen of 90 mg/kg/day divided into 2 doses when any of these risk factors are present: 1
  • Age < 2 years
  • Daycare attendance
  • Recent antibiotic use (within past 30 days)
  • Geographic area with > 10% penicillin-resistant S. pneumoniae
  • Moderate-to-severe illness presentation
• For a 16.78 kg child: 16.78 kg × 90 mg/kg/day = 1,510 mg/day total, which equals 755 mg per dose (approximately 7.5 mL twice daily). 1, 3
• This high-dose regimen achieves concentrations sufficient to overcome penicillin-resistant S. pneumoniae with MICs up to 2–4 mg/L. 1

Indication-Specific Dosing

Community-Acquired Pneumonia

• Children < 5 years old: Use 90 mg/kg/day in 2 doses (755 mg or 7.5 mL twice daily for this child) to ensure coverage of penicillin-resistant S. pneumoniae. 1, 3
• Treatment duration: 10 days for pneumonia, with clinical improvement expected within 48–72 hours. 1

Group A Streptococcal Pharyngitis

• Dose: 50–75 mg/kg/day in 2 doses for 10 days (maximum 1,000 mg per dose). 1
• For this 16.78 kg child: 840–1,260 mg/day total, which equals 420–630 mg per dose (approximately 4–6 mL twice daily). 1
• The full 10-day course must be completed to prevent acute rheumatic fever, even if symptoms resolve earlier. 1

Acute Bacterial Sinusitis

• Children ≥ 2 years without risk factors: 45 mg/kg/day (375 mg or 3.75 mL twice daily). 1
• Children < 2 years, daycare attendees, or recent antibiotic use: 80–90 mg/kg/day (755 mg or 7.5 mL twice daily). 1

Practical Administration Instructions

• Administer at the start of a meal to minimize gastrointestinal intolerance. 2
• Shake the suspension well before each use and measure doses accurately with an oral syringe or dosing cup. 2
• The suspension may be mixed with formula, milk, fruit juice, water, or cold drinks if needed, but must be consumed immediately after mixing. 2
• Refrigeration is preferable but not required; discard any unused suspension after 14 days. 2

Treatment Duration and Monitoring

• Minimum treatment duration: 48–72 hours beyond symptom resolution or evidence of bacterial eradication. 2
• For Streptococcus pyogenes infections: Minimum 10 days to prevent acute rheumatic fever. 1, 2
• For pneumonia: 10 days total, with reassessment if no improvement by 48–72 hours. 1
• If fever persists beyond 48–72 hours or the child deteriorates, consider atypical pathogens and reevaluate. 1

Common Pitfalls to Avoid

• Do not underdose in high-risk scenarios: Children < 2 years, daycare attendees, or those with recent antibiotic exposure require the 90 mg/kg/day regimen, not the standard 45 mg/kg/day dose. 1
• Do not use amoxicillin alone for β-lactamase-producing organisms: If H. influenzae or Moraxella catarrhalis with β-lactamase production is suspected, switch to amoxicillin-clavulanate (90 mg/kg/day of amoxicillin component). 1
• Do not exceed maximum doses: The maximum daily dose is 4,000 mg/day regardless of weight. 1
• Ensure completion of therapy: Parents must complete the full prescribed course even if symptoms improve, particularly for streptococcal infections. 1

When to Escalate Therapy

• If no clinical improvement occurs within 48–72 hours, consider: 1
  • Switching to amoxicillin-clavulanate for β-lactamase-producing organisms
  • Adding a macrolide (azithromycin) for atypical pathogens
  • Reevaluating the diagnosis and considering alternative pathogens or complications