What is the appropriate dose of amoxicillin (amoxicillin) for an 18.1 kg child with no known allergies to penicillin or amoxicillin and no impaired renal function, according to the British National Formulary for Children (BNFC) guidelines?

Amoxicillin Dosing for an 18.1 kg Child

For an 18.1 kg child, the standard amoxicillin dose is 408 mg twice daily (45 mg/kg/day divided every 12 hours) for mild to moderate infections, or 816 mg twice daily (90 mg/kg/day divided every 12 hours) for severe infections or areas with high pneumococcal resistance. 1

Weight-Based Calculation

• For this 18.1 kg child, the calculation is straightforward: 18.1 kg × 45 mg/kg/day = 814.5 mg/day total, administered as approximately 408 mg twice daily (every 12 hours) 1, 2
• For severe infections or high-resistance areas, the dose doubles: 18.1 kg × 90 mg/kg/day = 1,629 mg/day, administered as approximately 816 mg twice daily 1

Indication-Specific Dosing Algorithm

Mild to Moderate Respiratory Tract Infections

• The American Academy of Pediatrics recommends 45 mg/kg/day divided every 12 hours (approximately 408 mg twice daily for this patient) for uncomplicated respiratory tract infections, skin infections, and genitourinary infections. 1
• This provides adequate coverage for most susceptible pathogens including Streptococcus pneumoniae, Haemophilus influenzae (non-β-lactamase producing), and Streptococcus pyogenes 1

Severe Infections or High-Resistance Areas

• The Infectious Diseases Society of America recommends 90 mg/kg/day divided every 12 hours (approximately 816 mg twice daily) for community-acquired pneumonia in areas with >10% penicillin-resistant S. pneumoniae, children <2 years old, recent antibiotic exposure within the past 30 days, children attending daycare, or severe infections requiring hospitalization 1

Group A Streptococcal Infections

• For Group A Streptococcal pharyngitis, the American Heart Association recommends 50-75 mg/kg/day divided into 2 doses for 10 days, which translates to approximately 450-680 mg twice daily for this 18.1 kg child, not exceeding 1000 mg per dose 1

Practical Formulation Guidance

• Using the 250 mg/5 mL suspension: For 408 mg, administer approximately 8.2 mL twice daily 2
• Using the 125 mg/5 mL suspension: For 408 mg, administer approximately 16.3 mL twice daily 2
• The maximum daily dose should not exceed 4000 mg/day regardless of weight 1

Treatment Duration and Monitoring

• The standard treatment duration for most respiratory infections is 7-10 days, and for pneumonia specifically, 10 days of treatment is recommended 1
• Children on appropriate therapy should demonstrate clinical improvement within 48-72 hours; if no improvement occurs within this timeframe, reevaluation and further investigation are necessary 1
• For any infection caused by Streptococcus pyogenes, at least 10 days of treatment is required to prevent acute rheumatic fever 2

Critical Dosing Considerations

• For β-lactamase-producing organisms (H. influenzae, M. catarrhalis), switch to amoxicillin-clavulanate (Augmentin) at 90 mg/kg/day of the amoxicillin component rather than plain amoxicillin. 1
• Amoxicillin should be taken at the start of a meal to minimize gastrointestinal intolerance 2
• After reconstitution, oral suspension must be discarded after 14 days; refrigeration is preferable but not required 2