What is the appropriate dose of amoxicillin suspension 400 mg/5 mL for a child weighing 51 lb?

Amoxicillin Dosing for a 51-Pound Child

For a child weighing 51 pounds (23.1 kg), the appropriate dose of amoxicillin 400 mg/5 mL suspension is 5.75 mL (460 mg) twice daily for mild to moderate infections, or 10.4 mL (832 mg) twice daily for severe infections such as pneumonia or treatment-failure otitis media. 1

Weight-Based Dosing Calculation

• Standard dosing for mild to moderate infections: 20-25 mg/kg/day divided every 12 hours 1, 2

  • For a 23.1 kg child: 462-578 mg/day total
  • Per dose (twice daily): 231-289 mg per dose
  • Using 400 mg/5 mL suspension: 2.9-3.6 mL per dose 1

• High-dose for severe infections: 40-45 mg/kg/day divided every 12 hours 1, 2

  • For a 23.1 kg child: 924-1040 mg/day total
  • Per dose (twice daily): 462-520 mg per dose
  • Using 400 mg/5 mL suspension: 5.8-6.5 mL per dose 1

Clinical Context Determines Dose Selection

Use standard dosing (20-25 mg/kg/day) for: 1

• Uncomplicated otitis media
• Mild skin infections
• Uncomplicated urinary tract infections

Use high-dose (40-45 mg/kg/day) for: 1

• Community-acquired pneumonia
• Acute otitis media with recent antibiotic exposure or treatment failure
• Suspected penicillin-resistant Streptococcus pneumoniae
• Severe infections requiring hospitalization

Practical Administration

• Administer at the start of meals to minimize gastrointestinal intolerance 2
• Shake suspension well before each use 2
• The 400 mg/5 mL concentration allows precise weight-based dosing without requiring capsule manipulation 1
• Refrigeration is preferable but not required; discard unused suspension after 14 days 2

Critical Dosing Principles

• Always calculate pediatric doses based on actual body weight in kilograms (51 lb = 23.1 kg), never use adult fixed doses 1
• For children weighing >23-40 kg (>51-88 lb), the FDA-approved weight-band dosing is 60 mg twice daily for standard dosing, but this applies to the lower end of the dosing range and may be insufficient for severe infections 2
• Weight-based mg/kg dosing is more precise than weight-band dosing and should be prioritized, especially for severe infections 1

Common Pitfalls to Avoid

• Do not use adult fixed doses (500 mg or 875 mg) for children under 40 kg 1
• Do not use standard-dose amoxicillin (40-45 mg/kg/day) for acute otitis media, as it provides inadequate coverage against resistant S. pneumoniae—high-dose (80-90 mg/kg/day) is recommended 3
• Do not round to convenient volumes without ensuring the dose falls within the appropriate mg/kg range 1

Duration of Therapy

• Most infections require 7-10 days of treatment 1
• Streptococcal pharyngitis requires at least 10 days to prevent acute rheumatic fever 2
• Severe infections may require up to 14 days depending on clinical response 1