Dosing Calculation for Amoxicillin 400mg/5mL Suspension
For a 4-year-old child weighing 18 kg with acute otitis media, administer 8 mL of amoxicillin 400mg/5mL suspension per dose, given twice daily.
Calculation Breakdown
The recommended high-dose amoxicillin for acute otitis media is 80-90 mg/kg/day divided into 2 doses 1, 2, 3. This is the standard first-line treatment endorsed by major pediatric guidelines.
Step-by-step calculation:
- Target daily dose: 80-90 mg/kg/day
- For 18 kg child: 18 kg × 80 mg/kg = 1,440 mg/day (minimum)
- Divided into 2 doses: 1,440 mg ÷ 2 = 720 mg per dose
Converting to milliliters:
- Concentration: 400 mg per 5 mL
- This equals 80 mg per 1 mL
- For 720 mg: 720 mg ÷ 80 mg/mL = 9 mL per dose
However, using the more practical mid-range dosing of 85 mg/kg/day:
- 18 kg × 85 mg/kg = 1,530 mg/day
- Divided into 2 doses: 765 mg per dose
- Converting: 765 mg ÷ 80 mg/mL = 9.6 mL per dose (round to 9-10 mL)
For practical administration, 8-9 mL twice daily is appropriate, delivering approximately 640-720 mg per dose (1,280-1,440 mg/day total), which falls within the recommended 80-90 mg/kg/day range 3.
Key Clinical Points
- Timing: Administer every 12 hours (twice daily dosing) 3
- With food: Give at the start of meals to minimize gastrointestinal side effects 3
- Duration: Continue for minimum 10 days for otitis media 3
- Shake well: The suspension must be shaken vigorously before each dose 3
- Storage: Refrigeration is preferable but not required; discard after 14 days 3
Important Caveats
The FDA label specifies that for severe ear/nose/throat infections in children, the dose is 45 mg/kg/day in divided doses every 12 hours 3. However, current pediatric guidelines specifically for acute otitis media recommend the higher 80-90 mg/kg/day dosing to address increasingly resistant Streptococcus pneumoniae and Haemophilus influenzae 1, 2. The guideline-recommended high-dose regimen takes precedence over the general FDA dosing for AOM specifically.
If this child had received amoxicillin in the previous 30 days or has concurrent purulent conjunctivitis, amoxicillin-clavulanate would be preferred instead of amoxicillin alone 1.