What volume of a 400 mg per 5 mL amoxicillin oral suspension should be given to a child for a 10‑day course?

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Last updated: September 21, 2026 • View editorial policy

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Amoxicillin Dosing for Pediatric Infections

For a 10-day course using a 400 mg/5 mL suspension, the volume depends on the child's weight and the specific infection being treated, but for most common respiratory infections like acute otitis media (AOM) or community-acquired pneumonia (CAP), you should administer 90 mg/kg/day divided into two doses (45 mg/kg/dose twice daily).

Calculating the Volume

To determine the exact volume for each dose:

  1. Determine the child's weight in kg
  2. Calculate the dose: 45 mg/kg per dose (for twice-daily dosing)
  3. Convert to volume: Since the suspension is 400 mg/5 mL (or 80 mg/mL):
    • Volume (mL) = [Weight (kg) × 45 mg/kg] ÷ 80 mg/mL

Example Calculations:

  • 10 kg child: (10 × 45) ÷ 80 = 5.6 mL twice daily
  • 15 kg child: (15 × 45) ÷ 80 = 8.4 mL twice daily
  • 20 kg child: (20 × 45) ÷ 80 = 11.3 mL twice daily

Duration and Dosing Rationale

Duration: The standard 10-day course is recommended for children younger than 2 years and those with severe symptoms 1. For children 2-5 years with mild-to-moderate disease, 7 days may be sufficient, and for children ≥6 years with mild-to-moderate disease, guidelines still recommend 10 days 1.

High-dose rationale: The 90 mg/kg/day dosing (rather than the older 40-45 mg/kg/day standard) is critical for:

  • Adequate middle ear fluid penetration, particularly during viral coinfection 2
  • Coverage of penicillin-resistant Streptococcus pneumoniae 3
  • Achieving adequate time above MIC (minimum inhibitory concentration) 4

Twice-Daily vs Three-Times-Daily Dosing

Twice-daily dosing is preferred for several reasons:

  • Equivalent efficacy: Recent evidence demonstrates non-inferiority of twice-daily dosing compared to three-times-daily regimens 5
  • Better adherence: Families report significantly fewer difficulties with twice-daily schedules (5.8% vs 31% reporting scheduling problems) 5
  • Pharmacokinetic support: 25 mg/kg twice daily achieves adequate AUC and time above MIC 4

Critical Pitfalls to Avoid

  1. Underdosing with standard 40 mg/kg/day regimens: This is inadequate for resistant S. pneumoniae, especially during viral coinfection 2

  2. Using three-times-daily dosing unnecessarily: This reduces adherence without improving outcomes 5

  3. Incorrect volume calculation: Always verify your math—the 400 mg/5 mL concentration means you need more volume than with higher concentration suspensions

  4. Premature discontinuation: While 5-day courses show non-inferiority for uncomplicated CAP 6, 7, the 10-day course remains standard for AOM and for children <2 years 1

Storage and Administration

After reconstitution, store the suspension at 20°C to 25°C (68°F to 77°F) 8. The suspension should be shaken well before each dose and administered with or without food 8.

References

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This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.