What is the amoxicillin dose for a 100-pound pediatric patient?

Amoxicillin Dosing Calculation for 100-Pound Patient

For a 100-pound (45.4 kg) pediatric patient, the amoxicillin dose depends on the indication: for mild-to-moderate respiratory infections, administer 10.2 mL of 400mg/5mL suspension twice daily (45 mg/kg/day); for severe infections or high pneumococcal resistance areas, administer 20.4 mL twice daily (90 mg/kg/day). 1

Weight-Based Calculation

• The patient weighs 100 pounds, which converts to 45.4 kg 1
• For the 400mg/5mL suspension formulation, each mL contains 80 mg of amoxicillin 2

Standard Dosing Algorithm by Indication

Mild-to-Moderate Infections

• The American Academy of Pediatrics recommends 45 mg/kg/day divided every 12 hours for uncomplicated respiratory tract infections, skin infections, and genitourinary infections 1, 3
• Calculation: 45 mg/kg/day × 45.4 kg = 2,043 mg/day total, or 1,021 mg per dose twice daily 1
• Volume per dose: 1,021 mg ÷ 80 mg/mL = 12.8 mL, rounded to practical dosing of approximately 10-13 mL twice daily 1

Severe Infections or High-Resistance Areas

• The Infectious Diseases Society of America recommends 90 mg/kg/day divided every 12 hours for community-acquired pneumonia in areas with >10% penicillin-resistant S. pneumoniae, children <2 years old, recent antibiotic exposure within 30 days, daycare attendance, or severe infections 1, 3
• Calculation: 90 mg/kg/day × 45.4 kg = 4,086 mg/day total, or 2,043 mg per dose twice daily 1
• Volume per dose: 2,043 mg ÷ 80 mg/mL = 25.5 mL, rounded to practical dosing of approximately 20-25 mL twice daily 1

Group A Streptococcal Infections

• The American Heart Association recommends 50-75 mg/kg/day divided into 2 doses for 10 days, not exceeding 1,000 mg per dose 1, 3
• Calculation: 50-75 mg/kg/day × 45.4 kg = 2,270-3,405 mg/day total, or 1,135-1,702 mg per dose 1
• Since this exceeds the 1,000 mg maximum per dose, cap at 1,000 mg (12.5 mL) twice daily 1, 3

Critical Dosing Considerations

• The maximum daily dose of amoxicillin should not exceed 4,000 mg/day regardless of weight 1, 3
• At 45.4 kg, this patient is transitioning from pediatric to adult dosing parameters 4
• For patients weighing ≥40 kg with mild-to-moderate infections, the FDA-approved adult dose is 500 mg every 12 hours or 250 mg every 8 hours 2
• For severe infections in patients ≥40 kg, the FDA-approved dose is 875 mg every 12 hours or 500 mg every 8 hours 2

Treatment Duration and Monitoring

• Treatment duration should be 7-10 days for most respiratory infections, with pneumonia specifically requiring 10 days 1, 3
• For Group A Streptococcal infections, a mandatory 10-day course is required to prevent rheumatic fever 3, 2
• Clinical improvement should occur within 48-72 hours; if no improvement is seen, reassess the diagnosis and consider alternative antibiotics 1, 3

Important Clinical Pitfalls

• Twice-daily dosing improves adherence compared to three-times-daily regimens, making the every-12-hour schedule the preferred approach 3, 5
• The 400mg/5mL suspension must be shaken well before each use and refrigerated (though not required), with any unused portion discarded after 14 days 2
• For β-lactamase-producing organisms (H. influenzae, M. catarrhalis), switch to amoxicillin-clavulanate at 90 mg/kg/day of the amoxicillin component 1