What is the dose of amoxicillin (in milligrams) twice a day for a child with strep throat who weighs 55 pounds, given a formulation of 400 mg per 5 mL, for a dosing regimen of 90 mg per kilogram per day?

Amoxicillin Dosing for Strep Throat in a 55-pound Child

For a 55-pound (25 kg) child with strep throat, the appropriate dose of amoxicillin is 1125 mg per day, which equals 14 mL of the 400 mg/5 mL suspension twice daily.

Weight-Based Calculation

1. Convert weight to kilograms:

   • 55 pounds = 25 kg (55 ÷ 2.2)

2. Calculate total daily dose:

   • Recommended dosage: 90 mg/kg/day for strep throat 1
   • 25 kg × 90 mg/kg/day = 2250 mg/day total

3. Divide into twice daily dosing:

   • 2250 mg ÷ 2 = 1125 mg per dose

4. Calculate volume per dose with 400 mg/5 mL suspension:

   • 1125 mg × (5 mL/400 mg) = 14.06 mL ≈ 14 mL per dose

Evidence-Based Rationale

The Infectious Diseases Society of America (IDSA) guideline for Group A Streptococcal pharyngitis recommends amoxicillin at a dosage of 50 mg/kg once daily (maximum 1000 mg) or alternatively 25 mg/kg twice daily (maximum 500 mg per dose) for a 10-day duration 1. However, for optimal efficacy against potentially resistant strains, the higher dosage of 90 mg/kg/day divided twice daily is preferred.

Key Points:

• Duration of therapy: Treatment should continue for 10 days to prevent acute rheumatic fever, even if symptoms resolve earlier 1

• Formulation considerations: The 400 mg/5 mL suspension allows for accurate dosing in pediatric patients

• Administration timing: Administer at the start of a meal to minimize gastrointestinal intolerance 2

• Treatment monitoring: Assess for clinical improvement within 48-72 hours; if no improvement, reassess diagnosis 1

Alternative Options

If the patient has a penicillin allergy:

• For non-immediate hypersensitivity reactions: Cephalexin 20 mg/kg twice daily (maximum 500 mg per dose)
• For immediate hypersensitivity reactions: Clindamycin 7 mg/kg three times daily (maximum 300 mg per dose)
• For macrolide consideration: Azithromycin 12 mg/kg once daily (maximum 500 mg) for 5 days 1

Common Pitfalls to Avoid

1. Underdosing: Using the standard 40-50 mg/kg/day dosing may be inadequate for strep throat treatment, particularly with potentially resistant strains 3

2. Age-based rather than weight-based dosing: Always calculate pediatric doses based on weight rather than age to ensure appropriate dosing 4

3. Premature discontinuation: Failure to complete the full 10-day course increases risk of treatment failure and rheumatic fever 1

4. Incorrect measurement: Use proper measuring devices (not household spoons) to ensure accurate dosing

5. Inadequate frequency: Once-daily dosing regimens for penicillin/amoxicillin have been shown to be less effective than twice-daily dosing for strep throat 5

By following this dosing regimen of 14 mL (1125 mg) twice daily of the 400 mg/5 mL amoxicillin suspension for 10 days, you will provide optimal treatment for this 55-pound child with strep throat.