What is the appropriate dose (volume) of 400 mg/5 mL amoxicillin suspension for a 34‑lb (≈15 kg) child?

Amoxicillin Dosing for a 34-Pound Child

For a 34-pound (15.4 kg) child receiving amoxicillin 400 mg/5 mL suspension, the appropriate dose volume depends on the indication: for mild-to-moderate infections, administer 3.8 mL twice daily (45 mg/kg/day); for severe infections or pneumonia, administer 7.7 mL twice daily (90 mg/kg/day). 1

Dose Calculation by Indication

Mild-to-Moderate Infections (Ear/Nose/Throat, Skin, Uncomplicated UTI)

• Target dose: 45 mg/kg/day divided into 2 doses 1
• Calculation: 15.4 kg × 45 mg/kg/day = 693 mg/day
• Per-dose amount: 693 mg ÷ 2 = 346.5 mg per dose
• Volume per dose: 346.5 mg ÷ 80 mg/mL = 4.3 mL twice daily 1
• Alternatively, using 25 mg/kg/day divided every 12 hours yields approximately 3.8 mL twice daily 1

Severe Infections or Lower Respiratory Tract Infections (Pneumonia)

• Target dose: 90 mg/kg/day divided into 2 doses 2, 1
• Calculation: 15.4 kg × 90 mg/kg/day = 1,386 mg/day
• Per-dose amount: 1,386 mg ÷ 2 = 693 mg per dose
• Volume per dose: 693 mg ÷ 80 mg/mL = 8.7 mL twice daily 1
• Alternatively, using 45 mg/kg/day divided every 12 hours yields approximately 7.7 mL twice daily 1

Critical Dosing Considerations

High-Dose Amoxicillin Rationale

• The Infectious Diseases Society of America and Pediatric Infectious Diseases Society recommend 90 mg/kg/day for pneumococcal infections with penicillin MICs ≤2.0 μg/mL to ensure adequate coverage against resistant Streptococcus pneumoniae 2
• High-dose amoxicillin (80–90 mg/kg/day) is the preferred first-line therapy for community-acquired pneumonia in children 2, 3

Common Dosing Pitfalls

• Underdosing larger children: Research demonstrates that children weighing >15 kg frequently receive subtherapeutic doses because clinicians hesitate to exceed "adult maximum doses" 4
• At 15.4 kg, this child is at the threshold where many clinicians inappropriately cap the dose at 1,500 mg/day (the standard adult dose), resulting in only 97 mg/kg/day—adequate for this weight but problematic as the child grows 4, 5
• The FDA label does not specify an absolute maximum daily dose for children ≥3 months and <40 kg—dosing should be weight-based per indication 1

Administration Instructions

• Administer at the start of a meal to minimize gastrointestinal intolerance 1
• Shake suspension well before each use 1
• The suspension may be mixed with formula, milk, fruit juice, water, or cold drinks and must be consumed immediately 1
• Refrigeration is preferable but not required; discard unused suspension after 14 days 1

Duration of Therapy

• Minimum duration: Continue for 48–72 hours beyond symptom resolution or evidence of bacterial eradication 1
• Streptococcal infections: Treat for at least 10 days to prevent acute rheumatic fever 1
• Community-acquired pneumonia: Recent evidence supports 3-day courses as noninferior to 7-day courses for uncomplicated cases, though cough resolution may be slightly faster with 7 days 6, 7

When to Reassess or Escalate

• If no clinical improvement occurs within 48–72 hours, consider treatment failure due to resistant organisms (particularly MRSA or β-lactamase-producing Haemophilus influenzae) 2
• Second-line options include high-dose amoxicillin-clavulanate (80–90 mg/kg/day of amoxicillin component with maximum 6.4 mg/kg/day clavulanic acid) for β-lactamase producers 2
• For suspected MRSA or treatment failure, switch to clindamycin 30–40 mg/kg/day divided into 3 doses 2, 3