For a child weighing 56 kg who requires amoxicillin at 50 mg/kg/day, how many milliliters of a suspension containing 400 mg per 5 mL should be given per dose?

Amoxicillin Dosing Calculation for 56 kg Child

For a 56 kg child requiring amoxicillin 50 mg/kg/day using a 400 mg/5 mL suspension, give 17.5 mL per dose if divided twice daily, or 11.7 mL per dose if divided three times daily.

Calculation Breakdown

Total Daily Dose

• 56 kg × 50 mg/kg/day = 2,800 mg/day

Dosing Frequency Options

Twice Daily Dosing (Every 12 Hours):

• 2,800 mg ÷ 2 doses = 1,400 mg per dose
• 1,400 mg ÷ 400 mg/5 mL = 17.5 mL per dose

Three Times Daily Dosing (Every 8 Hours):

• 2,800 mg ÷ 3 doses = 933 mg per dose
• 933 mg ÷ 400 mg/5 mL = 11.7 mL per dose

Clinical Context for Dosing Frequency

The appropriate frequency depends on the indication 1, 2:

• For Group A Streptococcus pharyngitis: 50-75 mg/kg/day in 2 doses 1
• For pneumococcal infections (S. pneumoniae with MIC <2.0): 90 mg/kg/day in 2 doses or 45 mg/kg/day in 3 doses 2
• For H. influenzae (β-lactamase negative): 75-100 mg/kg/day in 3 doses 1, 2

At 50 mg/kg/day, twice-daily dosing (every 12 hours) is the standard approach 3. The FDA label confirms amoxicillin can be dosed every 12 hours for most indications 3.

Important Considerations

Weight-Based Dosing Alert

This child at 56 kg is receiving only 50 mg/kg/day. Recent evidence shows that larger children frequently receive subtherapeutic doses when clinicians cap doses at "adult maximums" 4. For many infections requiring high-dose therapy (particularly pneumococcal infections with intermediate resistance), guidelines recommend 80-90 mg/kg/day 1, 2.

Maximum Dose Ceiling

The FDA label indicates adult doses typically don't exceed 500 mg every 12 hours for mild-moderate infections or 875 mg every 12 hours for severe infections 3. At 56 kg receiving 1,400 mg per dose (twice daily), this child exceeds typical adult dosing but remains within appropriate weight-based parameters for severe infections.

Administration Instructions

• Give at the start of meals to minimize gastrointestinal intolerance 3
• Shake suspension well before each use 3
• Suspension remains stable for 14 days after reconstitution; refrigeration preferred but not required 3

Clinical Pitfall

The 50 mg/kg/day dose is lower than recommended for most serious bacterial infections in current guidelines. Verify the indication:

• If treating pneumococcal pneumonia or otitis media with intermediate penicillin resistance, increase to 80-90 mg/kg/day 1, 2
• If treating Group A Strep pharyngitis, 50 mg/kg/day is appropriate 1, 5
• If treating mild infections, this dose may be adequate 6