What is the appropriate amoxicillin dose for an 11‑month‑old child?

Amoxicillin Dosing for an 11-Month-Old Child

For an 11-month-old infant, prescribe amoxicillin at 45 mg/kg/day divided into two doses (every 12 hours) for mild-to-moderate respiratory tract infections, or 90 mg/kg/day divided into two doses for severe infections or areas with high pneumococcal resistance. 1

Standard Dosing Algorithm by Indication

Mild-to-Moderate Respiratory Tract Infections

• The American Academy of Pediatrics recommends 45 mg/kg/day divided every 12 hours for uncomplicated respiratory infections in infants older than 3 months. 1
• This regimen 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

• Prescribe 90 mg/kg/day divided every 12 hours when any of the following risk factors are present: 1
  • Age < 2 years (which includes your 11-month-old patient)
  • Daycare attendance
  • Recent antibiotic use within the past 30 days
  • Geographic area with > 10% penicillin-resistant S. pneumoniae
  • Moderate-to-severe illness presentation
• The Infectious Diseases Society of America endorses this high-dose regimen specifically for community-acquired pneumonia in children under 5 years to overcome penicillin-resistant S. pneumoniae. 1, 2

Group A Streptococcal Infections

• For pharyngitis or skin infections caused by Group A Streptococcus, prescribe 50–75 mg/kg/day divided into two doses for 10 days. 1
• The maximum single dose should not exceed 1,000 mg regardless of weight. 1

Practical Dosing Example

For a typical 11-month-old weighing approximately 9–10 kg:

• Mild-to-moderate infection: 45 mg/kg/day = 405–450 mg/day total, given as approximately 200–225 mg every 12 hours (4–4.5 mL of 250 mg/5 mL suspension twice daily). 1
• Severe infection or high-risk scenario: 90 mg/kg/day = 810–900 mg/day total, given as approximately 400–450 mg every 12 hours (8–9 mL of 250 mg/5 mL suspension twice daily). 1

Treatment Duration

• Continue therapy for a minimum of 48–72 hours beyond symptom resolution. 3
• For any infection caused by Streptococcus pyogenes, treat for at least 10 days to prevent acute rheumatic fever. 3
• For pneumonia, the standard duration is 7–10 days, with most guidelines recommending a full 10-day course. 1

When to Use Amoxicillin-Clavulanate Instead

Switch to amoxicillin-clavulanate (Augmentin) when β-lactamase-producing organisms are suspected: 1

• Incomplete Haemophilus influenzae type b vaccination status
• Concurrent purulent acute otitis media
• Recent antibiotic failure
• Known β-lactamase-producing H. influenzae or Moraxella catarrhalis

For these scenarios, prescribe amoxicillin-clavulanate at 90 mg/kg/day of the amoxicillin component divided into two doses (maximum 4 g/day). 1, 4

Special Considerations for Infants Under 12 Months

• The FDA label notes that for infants under 3 months (12 weeks), the maximum recommended dose is 30 mg/kg/day divided every 12 hours due to incompletely developed renal function. 3
• However, at 11 months of age, your patient falls into the standard pediatric dosing category (≥ 3 months), so the 45–90 mg/kg/day regimens apply. 1, 3
• The British Thoracic Society 2002 guidelines suggest lower doses that are now considered outdated; current evidence from the Infectious Diseases Society of America and American Academy of Pediatrics supports the higher 45–90 mg/kg/day dosing to address contemporary resistance patterns. 1

Critical Dosing Pitfalls to Avoid

• Do not underdose based on outdated guidelines—the 2002 British Thoracic Society recommendations are superseded by current IDSA/AAP guidance favoring higher doses. 5, 1
• Always use twice-daily dosing (every 12 hours) rather than three-times-daily for better adherence and comparable or superior pharmacokinetics. 1, 6
• Administer at the start of a meal to minimize gastrointestinal intolerance. 3
• Shake the oral suspension well before each dose and discard any unused portion after 14 days. 3

Monitoring and Follow-Up

• Children on appropriate antibiotic therapy should demonstrate clinical improvement within 48–72 hours. 1
• If no improvement occurs within this timeframe, reevaluate for treatment failure, consider atypical pathogens (and add a macrolide), or assess for complications requiring hospitalization. 1
• Fever typically resolves within 24–48 hours for pneumococcal infections, though cough may persist longer. 1