Dosing Amoxicillin 642.9 mg/5 mL for Otitis Media
For acute otitis media in children ≥3 months old, use 80-90 mg/kg/day of amoxicillin divided into 2 doses daily, which translates to approximately 0.6-0.7 mL per kg of body weight per day of the 642.9 mg/5 mL suspension, given in two divided doses.
Understanding the Formulation
The 642.9 mg/5 mL concentration is a high-dose amoxicillin-clavulanate formulation (14:1 ratio). This specific concentration contains:
- Amoxicillin: 600 mg/5 mL
- Clavulanate: 42.9 mg/5 mL
This formulation was specifically designed to deliver high-dose amoxicillin (90 mg/kg/day) while minimizing clavulanate exposure (6.4 mg/kg/day) to reduce diarrhea 1.
Dosing Algorithm
First-Line Treatment (Most Children)
- Target dose: 90 mg/kg/day of amoxicillin component
- Practical calculation: (Child's weight in kg × 0.75 mL) given twice daily
- Example: A 15 kg child receives 11.25 mL twice daily (total 22.5 mL/day = 2,700 mg amoxicillin/day = 90 mg/kg/day)
When to Use This High-Dose Formulation
Use the 642.9 mg/5 mL formulation when 1:
- Child received amoxicillin in the previous 30 days
- Concurrent purulent conjunctivitis (otitis-conjunctivitis syndrome)
- Coverage needed for β-lactamase-producing H. influenzae or M. catarrhalis
- Treatment failure after 48-72 hours on standard amoxicillin
Duration
- Standard: 10 days for children <2 years
- Alternative: 5-7 days for children ≥2 years with uncomplicated AOM 2
- Continue for minimum 48-72 hours after symptom resolution 2
Critical Dosing Considerations
Maximum Dose Limits
While guidelines recommend 80-90 mg/kg/day, do not exceed the standard adult dose of 1,500 mg/day (approximately 12.5 mL twice daily of this formulation) in heavier children 3. For children whose calculated dose exceeds this, prescribe the adult maximum dose.
Administration Instructions
- Give at the start of meals to minimize gastrointestinal side effects 2
- Shake well before each use
- Refrigeration preferred but not required
- Discard after 14 days 2
Common Pitfalls to Avoid
Underdosing in younger children: Primary care physicians frequently prescribe lower-than-recommended doses, particularly in children >20 kg 3. Use weight-based dosing consistently.
Confusion with standard amoxicillin: The 642.9 mg/5 mL formulation is NOT the same as standard amoxicillin suspensions (125 mg/5 mL or 250 mg/5 mL). This is a high-dose amoxicillin-clavulanate preparation.
Unnecessary use: If the child has NOT received antibiotics in the past 30 days and does NOT have concurrent conjunctivitis, standard high-dose amoxicillin alone (80-90 mg/kg/day) is preferred first-line therapy 1. The addition of clavulanate increases cost and diarrhea risk without added benefit in uncomplicated cases.
Clinical Outcomes
Treatment failure with amoxicillin for AOM is uncommon (2.2%), and recurrence occurs in only 3.3% of cases 4. Recent data show that amoxicillin remains effective despite increasing prevalence of β-lactamase-producing bacteria, with no difference in treatment failure between children with and without β-lactamase-producing pathogens 5. This supports continued use of standard amoxicillin as first-line therapy, reserving the 642.9 mg/5 mL formulation for specific indications listed above.
Practical Dosing Table
| Child Weight | Volume per Dose | Frequency |
|---|---|---|
| 10 kg | 7.5 mL | Twice daily |
| 15 kg | 11.25 mL | Twice daily |
| 20 kg | 12.5 mL* | Twice daily |
| >25 kg | 12.5 mL* | Twice daily |
*Maximum adult dose equivalent