Maximum Dose of Amoxicillin for a 9-Month-Old
For a 9-month-old infant, the maximum dose of amoxicillin is 90 mg/kg/day divided into 2 doses (or 45 mg/kg/day in 3 doses), with an absolute maximum of 4000 mg/day regardless of weight. 1, 2, 3
Standard Dosing Framework for Infants
High-dose amoxicillin at 90 mg/kg/day divided into 2 doses is the preferred regimen for treating community-acquired pneumonia and infections caused by resistant pathogens (including penicillin-resistant Streptococcus pneumoniae and β-lactamase-producing Haemophilus influenzae). 1, 2
The alternative dosing schedule is 45 mg/kg/day divided into 3 doses, which provides equivalent coverage but may have lower adherence due to more frequent administration. 1
For less severe infections (such as Group A Streptococcus pharyngitis), standard-dose amoxicillin at 50-75 mg/kg/day divided into 2 doses is appropriate. 1, 3
Age-Specific Considerations for Infants Under 12 Weeks
For infants younger than 3 months (12 weeks), the FDA-approved maximum dose is 30 mg/kg/day divided every 12 hours due to incompletely developed renal function. 4
Since your patient is 9 months old, this restriction does not apply, and the full 90 mg/kg/day dosing can be used. 4
Absolute Maximum Daily Dose
The FDA mandates an absolute maximum limit of 4000 mg/day of amoxicillin, regardless of the patient's weight. 2, 4
For a typical 9-month-old weighing 8-10 kg, the calculated dose would be 720-900 mg/day (at 90 mg/kg/day), which is well below this maximum threshold. 2
Indication-Specific Dosing
For community-acquired pneumonia with suspected resistant pathogens, prescribe 90 mg/kg/day in 2 divided doses. 1, 3
For β-lactamase-negative Haemophilus influenzae infections, use 75-100 mg/kg/day divided into 3 doses. 1
If β-lactamase-producing organisms are suspected, switch to amoxicillin-clavulanate at 90 mg/kg/day (based on the amoxicillin component) in 2 divided doses. 1, 2
Critical Dosing Pitfalls to Avoid
Do not underdose larger infants or toddlers by capping doses prematurely at "adult maximum" levels before reaching 4000 mg/day. Research demonstrates that children frequently receive subtherapeutic doses when clinicians inappropriately apply adult maximum doses to pediatric weight-based calculations. 5
Ensure adequate treatment duration of at least 48-72 hours beyond symptom resolution, with a minimum of 10 days for Streptococcus pyogenes infections to prevent acute rheumatic fever. 4
For oral suspension, verify that the prescribed volume can be completed within the 14-day stability window after reconstitution (refrigeration preferred but not required). 4, 6