Amoxicillin Dosing for 18-Month-Old, 20 lbs (9 kg)
For an 18-month-old child weighing 20 lbs (9 kg), the appropriate amoxicillin dose depends on the infection severity: for mild-to-moderate ear/nose/throat or skin infections, give 20-25 mg/kg/day divided every 8-12 hours (approximately 180-225 mg/day total, or 3.5-4.5 mL of 250 mg/5 mL suspension twice daily); for severe infections or lower respiratory tract infections, give 40-45 mg/kg/day divided every 8-12 hours (approximately 360-405 mg/day total, or 7-8 mL of 250 mg/5 mL suspension twice daily). 1
Practical Dosing Calculations
For your 250 mg/5 mL suspension:
Mild-to-Moderate Infections (Ear/Nose/Throat, Skin)
- Standard dosing: 20-25 mg/kg/day
- For 9 kg child: 180-225 mg/day total
- Twice daily (every 12 hours): Give 3.5-4.5 mL (90-112.5 mg) per dose
- Three times daily (every 8 hours): Give 2.5-3 mL (60-75 mg) per dose
Severe Infections or Lower Respiratory Tract
- High-dose: 40-45 mg/kg/day
- For 9 kg child: 360-405 mg/day total
- Twice daily (every 12 hours): Give 7-8 mL (180-200 mg) per dose
- Three times daily (every 8 hours): Give 5 mL (120-135 mg) per dose
Key Clinical Considerations
Age-specific guidance: Since this child is 18 months old (>12 weeks), they fall into the standard pediatric dosing category rather than the neonatal category, which has a maximum of 30 mg/kg/day. 1
Infection-specific dosing: The FDA label clearly distinguishes between mild/moderate and severe infections, with lower respiratory tract infections always requiring the higher dose range regardless of severity. 1 This aligns with IDSA/PIDS pneumonia guidelines recommending 90 mg/kg/day (divided into 2 doses of 45 mg/kg each) for pneumococcal pneumonia. 2
Twice vs. three times daily: Both dosing frequencies are acceptable and equivalent in efficacy. 3 Twice-daily dosing (every 12 hours) improves compliance and is increasingly preferred, particularly for high-dose regimens. 4 The total daily dose matters more than the frequency.
Common Pitfalls to Avoid
Underdosing in this weight range: Children in the 20 lb (9 kg) range are at particular risk of receiving inadequate doses because clinicians often cap doses at "adult maximums" prematurely. 5, 6 This child should receive weight-based dosing without artificial caps—the adult maximum of 1500 mg/day is irrelevant at this weight.
Pneumococcal resistance considerations: With increasing intermediate penicillin resistance in Streptococcus pneumoniae, high-dose amoxicillin (80-90 mg/kg/day) has become standard for suspected pneumococcal infections since 2014. 2, 7 For this 9 kg child with pneumonia, that translates to 720-810 mg/day total (14.4-16.2 mL of your suspension divided into 2 doses).
Duration: Continue treatment for minimum 48-72 hours beyond symptom resolution. For Streptococcus pyogenes infections, treat for at least 10 days to prevent acute rheumatic fever. 1 Recent evidence supports shorter 3-5 day courses for uncomplicated pneumonia, though 7-10 days remains standard. 8
Administration: Give at the start of meals to minimize gastrointestinal intolerance. 1 Shake suspension well before each dose. Refrigeration is preferable but not required; discard after 14 days. 1