Amoxicillin 400 mg/5 mL Dosing for Strep Throat in Children Over 40 kg
For a child weighing over 40 kg with streptococcal pharyngitis, give 12.5 mL of amoxicillin 400 mg/5 mL suspension twice daily for 10 days.
Dosing Calculation
The IDSA guideline recommends 50 mg/kg once daily (maximum 1000 mg) or 25 mg/kg twice daily (maximum 500 mg) for children with Group A streptococcal pharyngitis 1, 2.
For children over 40 kg:
- Twice-daily dosing: The maximum dose is 500 mg per dose
- With 400 mg/5 mL suspension: 500 mg ÷ 400 mg × 5 mL = 12.5 mL per dose
- Frequency: Give 12.5 mL twice daily (every 12 hours)
- Duration: 10 days (strong recommendation, high-quality evidence) 1, 2
Alternatively, if using once-daily dosing:
- Once-daily dosing: Maximum 1000 mg once daily
- Volume: 1000 mg ÷ 400 mg × 5 mL = 12.5 mL once daily
Key Clinical Considerations
The twice-daily regimen is preferred over once-daily because while research shows once-daily dosing can be effective 3, 4, 5, the IDSA guideline lists it as an "alternative" rather than preferred option 2. The FDA label also supports twice-daily dosing for this concentration 6.
Important pitfalls to avoid:
- Do not underdose larger children. Research demonstrates that children over 40 kg frequently receive subtherapeutic doses when clinicians are reluctant to exceed "adult maximum doses" 7. The 500 mg twice-daily maximum is appropriate and necessary for adequate treatment.
- Ensure the full 10-day course is completed to prevent acute rheumatic fever, even if symptoms resolve earlier 2, 6.
- Administer at the start of meals to minimize gastrointestinal side effects 6.
Shake the suspension well before each dose and refrigerate after reconstitution (though not required, it improves palatability) 6.