Amoxicillin Dosing for a 4-Year-Old Weighing 55 Pounds
For a 4-year-old child weighing 55 pounds (25 kg), the appropriate dose of amoxicillin 400 mg/5 mL suspension is 7 mL (560 mg) twice daily for most common infections, or 14 mL (1120 mg) twice daily for severe infections or high-resistance areas. 1
Standard Dosing Algorithm
For Mild to Moderate Respiratory Infections
- The recommended dose is 45 mg/kg/day divided into 2 doses, which equals 562.5 mg per dose (approximately 7 mL of 400 mg/5 mL suspension) twice daily for this 25 kg child 1
- This provides adequate coverage for most susceptible pathogens including Streptococcus pneumoniae, Haemophilus influenzae (non-β-lactamase producing), and Streptococcus pyogenes 1
For Severe Infections or High-Resistance Risk Factors
- The high-dose regimen is 90 mg/kg/day divided into 2 doses, which equals 1,125 mg per dose (approximately 14 mL of 400 mg/5 mL suspension) twice daily 1
- This higher dosing is indicated when any of the following risk factors are present: 1
- Age <2 years
- Daycare attendance
- Recent antibiotic use within the past 30 days
- Geographic area with >10% penicillin-resistant S. pneumoniae
- Severe infection requiring hospitalization
Indication-Specific Dosing
Community-Acquired Pneumonia
- Mild to moderate cases: 45 mg/kg/day (7 mL twice daily) 1
- Severe cases or high pneumococcal resistance: 90 mg/kg/day (14 mL twice daily) 1
- Treatment duration should be 10 days 1
Group A Streptococcal Infections (Scarlet Fever, Pharyngitis)
- The recommended dose is 50-75 mg/kg/day in 2 doses, which equals 625-937.5 mg per dose (approximately 8-12 mL twice daily) for 10 days 1
- Maximum dose per intake should not exceed 1000 mg 1
Acute Bacterial Sinusitis
- For children ≥2 years without risk factors: 45 mg/kg/day (7 mL twice daily) 1
- For children with risk factors (age <2 years, daycare, recent antibiotic use): 80-90 mg/kg/day (10-14 mL twice daily) 1
Critical Dosing Considerations
Maximum Daily Dose
- The maximum daily dose should not exceed 4000 mg/day regardless of weight 1
- For this 25 kg child, even the high-dose regimen (2,250 mg/day) is well below this maximum
When to Use Amoxicillin-Clavulanate Instead
- Switch to amoxicillin-clavulanate (Augmentin) at 90 mg/kg/day of the amoxicillin component if β-lactamase-producing organisms (H. influenzae, M. catarrhalis) are suspected 1, 2
- This is particularly important for children with incomplete Haemophilus influenzae type b vaccination or concurrent purulent acute otitis media 2
Treatment Duration and Monitoring
Expected Clinical Response
- Children on appropriate antibiotic therapy should show clinical improvement within 48-72 hours 1
- If no improvement is seen within this timeframe, reevaluation is necessary and consider switching antibiotics or investigating for complications 1
Standard Treatment Duration
- Most respiratory infections require 7-10 days of treatment 1
- Pneumonia specifically requires 10 days 1
- Group A Streptococcal infections require 10 days 1
Common Pitfalls to Avoid
Underdosing
- The old standard dose of 40 mg/kg/day is inadequate for eradicating resistant Streptococcus pneumoniae, particularly during viral coinfection 3
- Research demonstrates that 40 mg/kg/day results in insufficient middle ear fluid concentrations, with a dosing regimen of 75-90 mg/kg/day recommended for acute otitis media 3
Suspension Concentration Verification
- Always verify the suspension concentration before calculating volume 1
- The 400 mg/5 mL formulation is different from the 250 mg/5 mL or 125 mg/5 mL formulations commonly available
Compliance Issues
- Twice-daily dosing improves compliance compared to three-times-daily dosing 4
- The American College of Cardiology notes that amoxicillin has better taste and improved adherence due to twice-daily dosing compared to penicillin V 1