Amoxicillin Volume Calculation for Pediatric Otitis Media
Direct Answer
For a 400mg/5mL amoxicillin suspension, you need to know the child's weight to calculate the exact volume, as the recommended dose is 80-90 mg/kg/day divided into 2 doses. 1, 2
Dose Calculation Algorithm
Step 1: Determine Total Daily Dose
- Calculate 80-90 mg/kg/day based on the child's weight 3
- For example, a 19.5 kg (43 lb) child requires 1560-1755 mg/day total 1
- This translates to approximately 780-880 mg per dose (given twice daily) 1
Step 2: Convert to Volume Using 400mg/5mL Concentration
- The concentration is 80 mg/mL (400mg ÷ 5mL = 80 mg/mL)
- For 800 mg dose: 800 mg ÷ 80 mg/mL = 10 mL per dose 1
- For 900 mg dose: 900 mg ÷ 80 mg/mL = 11.25 mL per dose 1
Step 3: Practical Dosing Examples by Weight
- 10 kg child: 800-900 mg/day = 400-450 mg per dose = 5-5.6 mL twice daily 3, 2
- 15 kg child: 1200-1350 mg/day = 600-675 mg per dose = 7.5-8.4 mL twice daily 3, 2
- 20 kg child: 1600-1800 mg/day = 800-900 mg per dose = 10-11.25 mL twice daily 1, 2
Key Clinical Considerations
Why High-Dose Amoxicillin
- High-dose amoxicillin (80-90 mg/kg/day) is first-line treatment because it achieves middle ear fluid levels exceeding the MIC for intermediately resistant and many highly resistant S. pneumoniae strains 3
- This dosing provides superior bacteriologic efficacy compared to standard dosing (40 mg/kg/day), with 87% susceptibility versus 83% for drug-resistant pneumococcus 3
When to Switch from Standard Amoxicillin
- Use amoxicillin-clavulanate (90 mg/kg/day of amoxicillin component with 6.4 mg/kg/day clavulanate) if the child received amoxicillin in the previous 30 days, has concurrent purulent conjunctivitis, or needs coverage for β-lactamase-producing H. influenzae or M. catarrhalis 3, 2
- The 14:1 ratio formulation causes less diarrhea than other preparations 3
Treatment Duration
- 5-10 days depending on age and severity, with 5 days sufficient for children over 2 years with uncomplicated AOM 1
Reassessment Criteria
- Reassess at 48-72 hours if symptoms fail to improve 1, 2
- Switch to amoxicillin-clavulanate or ceftriaxone if no improvement by 48-72 hours 1, 2
Common Pitfalls to Avoid
- Do not underdose: Using standard 40 mg/kg/day dosing instead of high-dose 80-90 mg/kg/day reduces efficacy against resistant S. pneumoniae 3
- Do not use the 400mg/5mL concentration if prescribing amoxicillin-clavulanate: The high-dose formulation requires specific ratios (14:1) to minimize diarrhea 3
- Do not continue amoxicillin monotherapy if the child received it within 30 days: Switch directly to amoxicillin-clavulanate 3, 2