What is the recommended dose of amoxicillin (amoxicillin) for a 3-month-old baby?

Amoxicillin Dosing for a 3-Month-Old Infant

For a 3-month-old infant, the recommended dose of amoxicillin is 30 mg/kg/day divided every 12 hours for most common infections, with this upper limit specifically established due to incompletely developed renal function in this age group. 1

Age-Specific Dosing Considerations

Standard Dosing for Infants Under 3 Months

• The maximum recommended dose is 30 mg/kg/day divided into two doses (every 12 hours) due to immature renal function affecting amoxicillin elimination 1
• This dosing applies to infants less than 12 weeks (3 months) of age 1
• Treatment should continue for a minimum of 48-72 hours beyond symptom resolution or evidence of bacterial eradication 1

Infection-Specific Dosing at 3 Months

For urinary tract infections in infants 8-21 days old:

• Ampicillin IV/IM (150 mg/kg/day divided every 8 hours) PLUS either ceftazidime or gentamicin is preferred over oral amoxicillin 2

For suspected bacteremia without identified focus in infants 8-21 days old:

• Parenteral therapy with ampicillin plus ceftazidime or gentamicin is recommended rather than oral amoxicillin 2

Transition Point at 3 Months

Once the infant reaches exactly 3 months of age (12 weeks) and weighs less than 40 kg, dosing increases significantly:

• Mild/moderate infections: 25 mg/kg/day divided every 12 hours OR 20 mg/kg/day divided every 8 hours 1
• Severe infections or lower respiratory tract infections: 45 mg/kg/day divided every 12 hours OR 40 mg/kg/day divided every 8 hours 1

Clinical Context and Pitfalls

Important Caveats

• The 30 mg/kg/day limit for infants under 3 months is a critical safety threshold that should not be exceeded due to immature renal clearance 1
• For serious infections in this age group, parenteral antibiotics are generally preferred over oral amoxicillin 2
• Amoxicillin should be taken at the start of a meal to minimize gastrointestinal intolerance 1

When to Use Higher Doses

• Do NOT use the higher pediatric doses (45-90 mg/kg/day) in infants under 3 months regardless of infection severity 1
• If higher antibiotic coverage is needed, switch to parenteral therapy rather than increasing oral amoxicillin dose 2

Duration of Therapy

• Minimum 48-72 hours beyond clinical improvement 1
• For Streptococcus pyogenes infections, at least 10 days of treatment is required to prevent acute rheumatic fever 1
• Some infections may require several weeks of therapy with extended clinical follow-up 1

Practical Administration

Oral Suspension Preparation

• Reconstituted suspension must be shaken well before each use 1
• Unused reconstituted suspension must be discarded after 14 days 1
• Refrigeration is preferable but not required 1
• Can be mixed with formula, milk, fruit juice, or water and administered immediately 1