What is the recommended dose of amoxicillin (amoxicillin) for a 5-month-old baby?

Amoxicillin Dosing for a 5-Month-Old Baby

For a 5-month-old infant, the recommended dose of amoxicillin is 30 mg/kg/day divided every 12 hours (15 mg/kg per dose twice daily), with a maximum of 30 mg/kg/day due to incompletely developed renal function in this age group. 1

Standard Dosing Guidelines

The FDA-approved dosing for infants under 12 weeks (3 months) specifically addresses the unique pharmacokinetic considerations in this age group 1:

• Maximum daily dose: 30 mg/kg/day divided every 12 hours 1
• Individual dose: 15 mg/kg per dose, given twice daily 1
• Rationale: Incompletely developed renal function affects amoxicillin elimination in infants under 3 months 1

While your 5-month-old technically falls outside the "under 3 months" category, the dosing transitions gradually. For infants 3 months and older weighing less than 40 kg, standard dosing increases to 2, 1:

• Mild to moderate infections: 40-90 mg/kg/day in 2-3 divided doses 2
• Standard regimen: 25 mg/kg/dose every 12 hours OR 20 mg/kg/day every 8 hours 2, 1

Infection-Specific Considerations

Important caveat: For serious infections in infants under 3 months (and this caution often extends to young infants under 6 months), parenteral antibiotics are generally preferred over oral amoxicillin 3:

• Urinary tract infections: Ampicillin IV/IM (150 mg/kg/day divided every 8 hours) PLUS ceftazidime or gentamicin is recommended over oral amoxicillin 3
• Suspected bacteremia: Parenteral therapy with ampicillin plus ceftazidime or gentamicin is preferred 3
• Serious infections: Parenteral antibiotics are generally preferred in infants under 3 months 3

Practical Dosing Example

For a typical 5-month-old weighing approximately 7 kg:

• Conservative approach (using under-3-month guidelines): 15 mg/kg × 7 kg = 105 mg per dose, twice daily 1
• Standard approach (using 3+ month guidelines): 20-25 mg/kg × 7 kg = 140-175 mg per dose, twice daily 2, 1

Duration of Treatment

• Minimum duration: 48-72 hours beyond symptom resolution or evidence of bacterial eradication 1
• Streptococcus pyogenes infections: Minimum 10 days to prevent acute rheumatic fever 1
• Respiratory infections: Typically 7-10 days 4

Administration Guidelines

• Timing: Give at the start of a meal to minimize gastrointestinal intolerance 1
• Preparation: Oral suspension should be shaken well before each use 1
• Storage: Refrigeration is preferable but not required; discard unused suspension after 14 days 1

Critical Safety Considerations

When to use parenteral therapy instead: If the infant has signs of serious infection (fever, poor feeding, lethargy, respiratory distress), parenteral antibiotics should be strongly considered rather than oral amoxicillin 3. The threshold for hospitalization and IV antibiotics is lower in young infants due to their immature immune systems and rapid potential for clinical deterioration.

Monitoring: Children should show clinical improvement within 48-72 hours; if no improvement occurs, reevaluation is necessary 4.