What is the appropriate amoxicillin dosage for a 6‑year‑old boy weighing 34 lb (≈15.4 kg) with a bacterial respiratory infection?

Amoxicillin Dosing for a 6-Year-Old with Respiratory Infection

For a 6-year-old boy weighing 34 lbs (15.4 kg) with a bacterial respiratory infection, prescribe amoxicillin 90 mg/kg/day divided into two doses (approximately 690 mg per dose, or 1,380 mg total daily) for 10 days. 1, 2

Weight-Based Calculation

• The child weighs 34 lbs, which equals 15.4 kg (34 ÷ 2.2 = 15.4 kg). 2
• At 90 mg/kg/day: 15.4 kg × 90 mg = 1,386 mg total daily dose. 1, 2
• Divided into two doses: 693 mg per dose, administered every 12 hours. 1, 2
• Using a 400 mg/5 mL suspension: approximately 8.7 mL twice daily (round to 9 mL for practical administration). 2

Rationale for High-Dose Regimen

• High-dose amoxicillin (90 mg/kg/day) is the recommended first-line therapy for presumed bacterial community-acquired pneumonia in children over 3 months to ensure adequate coverage of penicillin-resistant Streptococcus pneumoniae, the most common bacterial pathogen in this age group. 1, 2
• This dosing achieves tissue concentrations sufficient to overcome organisms with penicillin MICs up to 2–4 mg/L, which standard-dose amoxicillin (45 mg/kg/day) cannot reliably achieve. 2, 3
• The twice-daily schedule maintains therapeutic drug levels throughout the dosing interval while improving adherence compared to three-times-daily regimens. 1, 2

Treatment Duration

• Complete a full 10-day course for bacterial respiratory infections, regardless of symptom improvement. 1, 2, 4
• Continue therapy for at least 48–72 hours after complete resolution of fever and respiratory symptoms. 2, 4

When to Switch to Amoxicillin-Clavulanate

Consider switching to amoxicillin-clavulanate (90 mg/kg/day of amoxicillin component + 6.4 mg/kg/day clavulanate, divided twice daily) if any of the following apply:

• No clinical improvement or worsening after 48–72 hours of amoxicillin therapy. 1, 2, 4
• Incomplete immunization against Haemophilus influenzae type b or Streptococcus pneumoniae. 1, 2, 4
• Recent antibiotic exposure within the past 30 days. 2, 5
• Concurrent purulent acute otitis media. 2, 4
• Suspected β-lactamase-producing organisms (H. influenzae, Moraxella catarrhalis). 1, 2, 5

Expected Clinical Response & Monitoring

• Fever should resolve within 24–48 hours after starting appropriate antibiotic therapy. 2, 4
• Overall clinical improvement (reduced respiratory distress, better feeding, decreased cough) should be evident within 48–72 hours. 1, 2, 4
• Mandatory reassessment at 48–72 hours if any of the following occur: persistent or worsening fever, deterioration of respiratory symptoms, oxygen saturation ≤ 92%, inability to maintain oral intake, or altered mental status. 2, 4

When to Consider Atypical Pathogens

• At age 6 years, atypical organisms (Mycoplasma pneumoniae, Chlamydophila pneumoniae) become more prevalent, but typical bacterial pathogens remain most common. 1, 4
• If no improvement after 48–72 hours of amoxicillin, add azithromycin (10 mg/kg on day 1, then 5 mg/kg daily on days 2–5) to cover atypical bacteria. 1, 2, 4
• Obtain chest radiography to exclude complications such as empyema if clinical response is inadequate. 4

Critical Pitfalls to Avoid

• Do not use twice-daily dosing of 45 mg/kg/day for respiratory infections in this age group; the 90 mg/kg/day regimen is required for adequate pneumococcal coverage. 1, 2
• Do not prescribe antibiotics for mild respiratory symptoms without clear evidence of bacterial infection, as most cases are viral. 4, 6
• Do not discontinue antibiotics early even if symptoms improve; completing the full 10-day course is essential to prevent relapse and reduce resistance. 2, 4
• Chest physiotherapy provides no benefit in pediatric pneumonia and should be omitted. 4
• First-generation cephalosporins (e.g., cephalexin) have inadequate activity against respiratory pathogens and should not be substituted. 4

Practical Administration

• Administer amoxicillin at the start of a meal to minimize gastrointestinal intolerance. 7
• Shake the suspension well before each dose. 7
• Refrigeration is preferable but not required; discard any unused suspension after 14 days. 7
• Common adverse effects include diarrhea, nausea, and rash (occurring in approximately 38% of patients). 2