What is the recommended dosing of amoxicillin (amoxicillin) 100mg/mL for a 3-month-old child weighing 5.5kg?

Amoxicillin Dosing for a 3-Month-Old Infant Weighing 5.5kg

For a 3-month-old infant weighing 5.5kg, the recommended dose of amoxicillin 100mg/mL oral suspension is 2.5 mL twice daily (total daily dose of 45 mg/kg/day) for mild to moderate respiratory infections, or 5 mL twice daily (total daily dose of 90 mg/kg/day) for severe infections or areas with high pneumococcal resistance. 1

Dosing Calculation

• Mild to moderate infections: 45 mg/kg/day divided into 2 doses

  • 5.5 kg × 45 mg/kg/day = 247.5 mg/day
  • 247.5 mg ÷ 2 doses = 123.75 mg per dose
  • Using 100 mg/mL suspension: 123.75 mg ÷ 100 mg/mL = 1.2 mL per dose (can round to 1.25 mL for practical administration) 1

• Severe infections or high resistance areas: 90 mg/kg/day divided into 2 doses

  • 5.5 kg × 90 mg/kg/day = 495 mg/day
  • 495 mg ÷ 2 doses = 247.5 mg per dose
  • Using 100 mg/mL suspension: 247.5 mg ÷ 100 mg/mL = 2.5 mL per dose 2, 1

Critical Age-Specific Considerations

For infants younger than 3 months (12 weeks), the FDA label recommends a maximum dose of 30 mg/kg/day divided every 12 hours due to incompletely developed renal function affecting amoxicillin elimination. 3 Since this child is exactly 3 months old, standard pediatric dosing applies, but close monitoring is warranted given proximity to this age threshold.

Indication-Based Dosing

• Community-acquired pneumonia (mild to moderate): 45 mg/kg/day in 2 doses = approximately 1.25 mL twice daily 2, 1
• Community-acquired pneumonia (severe) or high pneumococcal resistance: 90 mg/kg/day in 2 doses = 2.5 mL twice daily 2, 1
• Group A Streptococcal infections: 50-75 mg/kg/day in 2 doses = 1.4-2.1 mL twice daily 1

Treatment Duration and Monitoring

• Standard treatment duration is 10 days for most respiratory infections, particularly pneumonia. 2
• For Streptococcus pyogenes infections, a minimum 10-day course is mandatory to prevent acute rheumatic fever. 3
• Children on appropriate therapy should demonstrate clinical improvement within 48-72 hours; if no improvement occurs, reevaluation and further investigation are necessary. 2

Administration Guidelines

• Administer at the start of a meal to minimize gastrointestinal intolerance. 3
• Shake the suspension well before each use. 3
• The suspension can be placed directly on the child's tongue or mixed with formula or milk for immediate administration. 3
• Store reconstituted suspension in refrigerator (preferred but not required) and discard after 14 days. 3

Common Pitfalls to Avoid

• Do not underdose: The 45 mg/kg/day regimen is appropriate for mild infections, but severe infections or areas with high pneumococcal resistance require 90 mg/kg/day 2, 1
• Do not use the lower dose (30 mg/kg/day) recommended for infants under 3 months unless specifically indicated by renal impairment 3
• Ensure completion of the full antibiotic course even if symptoms improve before completion 1
• Most common adverse effects include gastrointestinal disturbances (diarrhea, nausea, vomiting) and potential hypersensitivity reactions 1