What is the recommended dose of Amoxicillin (amoxicillin) for a 45-pound pediatric patient?

Amoxicillin Dosing for a 45-Pound Pediatric Patient

For a 45-pound (20.4 kg) child, prescribe amoxicillin 400mg/5ml suspension at 5 mL twice daily (45 mg/kg/day) for mild to moderate infections, or 10 mL twice daily (90 mg/kg/day) for severe infections or high pneumococcal resistance areas. 1

Weight-Based Calculation

• A 45-pound child weighs 20.4 kg 1

• For mild to moderate respiratory infections, the American Academy of Pediatrics recommends 45 mg/kg/day divided every 12 hours 1, 2

  • Calculation: 20.4 kg × 45 mg/kg/day = 918 mg/day
  • Per dose: 459 mg twice daily ≈ 460 mg (5.75 mL) twice daily using 400mg/5ml suspension 1
  • Practical dosing: 5 mL twice daily (400 mg per dose, 800 mg/day = 39 mg/kg/day) 1

• For severe infections or high pneumococcal resistance areas, the Infectious Diseases Society of America recommends 90 mg/kg/day divided every 12 hours 1, 2

  • Calculation: 20.4 kg × 90 mg/kg/day = 1,836 mg/day
  • Per dose: 918 mg twice daily
  • Practical dosing: 10 mL twice daily (800 mg per dose, 1,600 mg/day = 78 mg/kg/day) 1

Indication-Specific Dosing Algorithm

For mild to moderate infections (uncomplicated respiratory tract infections, skin infections, genitourinary infections):

• Prescribe 45 mg/kg/day divided every 12 hours 1, 3
• 5 mL of 400mg/5ml suspension twice daily 1

For severe infections or high-resistance scenarios (community-acquired pneumonia in high-resistance areas, children <2 years, recent antibiotic exposure, daycare attendance):

• Prescribe 90 mg/kg/day divided every 12 hours 1, 2, 4
• 10 mL of 400mg/5ml suspension twice daily 1, 2

For Group A Streptococcal infections (pharyngitis, scarlet fever):

• The Infectious Diseases Society of America recommends 50-75 mg/kg/day divided into 2 doses for 10 days 1, 2
• 6.25-7.5 mL of 400mg/5ml suspension twice daily 2
• Maximum 1000 mg per dose 2

Critical Dosing Considerations

• The maximum daily dose should not exceed 4000 mg/day regardless of weight 1, 2
• At 20.4 kg, this child is well below the 40 kg threshold where adult dosing begins 3
• Twice-daily dosing improves adherence compared to three-times-daily regimens 1
• The FDA label confirms that for children <40 kg with severe infections, 45 mg/kg/day divided every 12 hours is appropriate 3

Treatment Duration

• Continue treatment for a minimum of 48-72 hours beyond symptom resolution 1, 3
• For respiratory infections, treat for 7-10 days 1, 2
• For pneumonia specifically, treat for 10 days 1, 2
• For Group A Streptococcal infections, mandatory 10-day course to prevent rheumatic fever 1, 2

When to Use Higher Dosing (90 mg/kg/day)

The Infectious Diseases Society of America and American Academy of Pediatrics recommend high-dose amoxicillin for: 2, 4

• Community-acquired pneumonia in areas with >10% penicillin-resistant S. pneumoniae
• Children <2 years old with pneumonia
• Recent antibiotic exposure within the past 30 days
• Children attending daycare
• Severe infections requiring hospitalization

Administration Instructions

• Administer at the start of a meal to minimize gastrointestinal intolerance 3
• Shake suspension well before each use 3
• Refrigeration is preferable but not required 3
• Discard unused suspension after 14 days 3

Monitoring and Follow-Up

• Clinical improvement should occur within 48-72 hours 1, 2
• If no improvement by 72 hours, reassess diagnosis and consider alternative antibiotics 1, 2
• Complete the full prescribed course even if symptoms improve 1

Common Pitfalls to Avoid

• Do not underdose larger children: Research demonstrates that children >60 kg frequently receive <40 mg/kg/day when they should receive guideline-recommended doses 5
• Do not use amoxicillin alone for β-lactamase-producing organisms: Switch to amoxicillin-clavulanate for H. influenzae or M. catarrhalis 2
• Do not use amoxicillin if MRSA is suspected: Amoxicillin provides no coverage for MRSA 1