What is the recommended dose of amoxicillin (amoxicillin) for a 4-month-old infant weighing 6 kg?

Amoxicillin Dosing for a 4-Month-Old Infant Weighing 6 kg

For a 4-month-old infant weighing 6 kg, administer amoxicillin at 45 mg/kg/day divided into 2 doses (every 12 hours), which equals 270 mg per day or 135 mg per dose, translating to 1.35 mL of the 100 mg/mL suspension twice daily for mild to moderate infections. 1, 2

Dose Calculation and Administration

• The American Academy of Pediatrics recommends 45 mg/kg/day divided every 12 hours for mild to moderate respiratory infections in infants over 3 months of age 1, 2

• For this 6 kg infant:

  • Total daily dose: 6 kg × 45 mg/kg = 270 mg/day
  • Per dose (twice daily): 270 mg ÷ 2 = 135 mg per dose
  • Volume per dose with 100 mg/mL suspension: 135 mg ÷ 100 mg/mL = 1.35 mL twice daily 1, 2

• Administer at the start of a meal to minimize gastrointestinal intolerance 3

Dosing Based on Infection Severity

• For mild to moderate infections (most common respiratory tract infections, skin infections, uncomplicated urinary tract infections): Use 45 mg/kg/day divided every 12 hours 1, 2

• For severe infections or areas with high pneumococcal resistance: Increase to 90 mg/kg/day divided every 12 hours, which would be 540 mg/day or 270 mg per dose (2.7 mL twice daily) for this 6 kg infant 1, 2

• The FDA label confirms that for severe infections in pediatric patients, 45 mg/kg/day divided every 12 hours or 40 mg/kg/day divided every 8 hours is appropriate 3

Treatment Duration and Monitoring

• Continue treatment for a minimum of 48-72 hours beyond symptom resolution or evidence of bacterial eradication 1, 3

• For most respiratory infections, treat for 7-10 days, with pneumonia specifically requiring 10 days 1, 2

• For Group A Streptococcal infections, 10 days of treatment is mandatory to prevent acute rheumatic fever 2, 3

• Clinical improvement should occur within 48-72 hours; if no improvement is seen, reassess the diagnosis and consider alternative antibiotics 1, 2

Critical Considerations for This Age Group

• At 4 months of age, this infant is just above the 3-month (12-week) threshold where standard pediatric dosing applies rather than neonatal dosing 3

• Infants under 3 months have incompletely developed renal function, requiring a maximum dose of 30 mg/kg/day divided every 12 hours, but this 4-month-old can receive standard pediatric dosing 3

• The twice-daily dosing regimen (every 12 hours) significantly improves adherence compared to three-times-daily regimens 2, 4

Common Pitfalls to Avoid

• Do not use age-based dosing—always calculate based on current body weight 4

• Shake the suspension well before each use and ensure proper reconstitution of the powder 3

• The reconstituted suspension must be discarded after 14 days; refrigeration is preferable but not required 3

• Most common adverse effects include gastrointestinal disturbances (diarrhea, nausea, vomiting) and potential hypersensitivity reactions (rash, urticaria) 1, 2

Prescription Documentation

• Every prescription should clearly state: the total daily dose in mg/kg/day (45 mg/kg/day), number of divided doses (2 doses per day), duration of therapy, indication for prescription, and the child's weight (6 kg) 2, 4