Amoxicillin Dosing for 150-Day-Old Infant Weighing 3.78 kg
For a 150-day-old (approximately 5 months) infant weighing 3.78 kg, the recommended dose of amoxicillin suspension is 30 mg/kg/day divided every 12 hours, which equals approximately 57 mg (or 1.9 mL of 125 mg/5 mL suspension) twice daily for mild to moderate infections. 1
Weight-Based Dosing Calculation
For infants under 12 weeks (3 months): The FDA-approved maximum dose is 30 mg/kg/day divided every 12 hours due to incompletely developed renal function 1
For infants 3 months and older weighing less than 40 kg: Standard dosing is 20-25 mg/kg/day for mild/moderate infections or 40-45 mg/kg/day for severe infections, divided every 8-12 hours 1
Since this patient is 150 days old (approximately 5 months), they fall into the 3+ months category 1
Specific Dose Recommendations by Severity
For Mild to Moderate Infections (Ear/Nose/Throat, Skin, Genitourinary):
- 25 mg/kg/day divided every 12 hours 1
- For 3.78 kg: 25 × 3.78 = 94.5 mg/day = 47 mg per dose twice daily 1
- Using 125 mg/5 mL suspension: 1.9 mL twice daily 1
For Severe Infections or Lower Respiratory Tract Infections:
- 45 mg/kg/day divided every 12 hours 1
- For 3.78 kg: 45 × 3.78 = 170 mg/day = 85 mg per dose twice daily 1
- Using 125 mg/5 mL suspension: 3.4 mL twice daily 1
Clinical Context and Indication-Specific Dosing
For community-acquired pneumonia (mild to moderate): The American Academy of Pediatrics recommends 45 mg/kg/day in 2 doses 2
For severe pneumonia or high pneumococcal resistance areas: 90 mg/kg/day in 2 doses may be warranted 2
For Group A Streptococcal infections: 50-75 mg/kg/day divided into 2 doses for 10 days 2
Administration Guidelines
Administer at the start of a meal to minimize gastrointestinal intolerance 1
Suspension preparation: After reconstitution, place the required amount directly on the child's tongue or mix with formula, milk, or fruit juice and administer immediately 1
Storage: Shake well before each use; refrigeration is preferable but not required; discard unused portion after 14 days 1
Treatment Duration
Continue treatment for a minimum of 48-72 hours beyond symptom resolution or evidence of bacterial eradication 1
For Streptococcus pyogenes infections: At least 10 days of treatment is required to prevent acute rheumatic fever 1
For respiratory infections including pneumonia: Standard duration is 7-10 days, with pneumonia specifically requiring 10 days 2
Critical Safety Considerations
This infant's weight (3.78 kg) is significantly below the expected weight for a 5-month-old (typically 6-8 kg), which may indicate failure to thrive or prematurity 3
Patient weight in kilograms should always be included on prescriptions to allow pharmacists to verify appropriate dosing 3
Monitor for clinical improvement within 48-72 hours; if no improvement occurs, reevaluation and further investigation are necessary 2
Common Pitfalls to Avoid
Do not use the 875 mg tablet formulation in pediatric patients or those with severe renal impairment 1
Avoid extrapolating term infant dosing to premature infants due to immature renal function and risk of drug accumulation 4
Do not assume standard adult dosing for weight-based pediatric calculations 3
Ensure accurate weight measurement as even small errors significantly impact dosing in low-weight infants 3