What is the recommended dosage of Amoxicillin (amoxicillin) for an 8-year-old patient weighing 98 pounds?

Amoxicillin Dosing for an 8-Year-Old Weighing 98 Pounds

For an 8-year-old child weighing 98 pounds (44.5 kg), the recommended amoxicillin dose depends on the indication: for mild to moderate respiratory tract infections, prescribe 45 mg/kg/day divided into 2 doses (approximately 1000 mg twice daily or 10 mL of 400mg/5mL suspension twice daily), while for severe infections or areas with high pneumococcal resistance, prescribe 90 mg/kg/day divided into 2 doses (approximately 2000 mg twice daily or 20 mL of 400mg/5mL suspension twice daily). 1

Weight-Based Calculation

• Patient weight: 98 pounds = 44.5 kg
• Standard dose (45 mg/kg/day): 44.5 kg × 45 mg/kg = 2002.5 mg/day, divided into 2 doses = approximately 1000 mg per dose 1
• High dose (90 mg/kg/day): 44.5 kg × 90 mg/kg = 4005 mg/day, divided into 2 doses = approximately 2000 mg per dose 1
• Using 400mg/5mL suspension: Standard dose = 12.5 mL twice daily; High dose = 25 mL twice daily 2

Indication-Specific Dosing Algorithm

For Mild to Moderate Infections

• Uncomplicated respiratory tract infections, skin infections, or genitourinary infections: 45 mg/kg/day divided every 12 hours (approximately 1000 mg twice daily) 1
• This provides adequate coverage for most susceptible pathogens including Streptococcus pneumoniae, Haemophilus influenzae (non-β-lactamase producing), and Streptococcus pyogenes 1

For Severe Infections or High-Risk Situations

• Use 90 mg/kg/day divided every 12 hours (approximately 2000 mg twice daily) if ANY of the following apply: 1
  • Community-acquired pneumonia in areas with >10% penicillin-resistant S. pneumoniae 1
  • Recent antibiotic exposure within the past 30 days 1
  • Daycare attendance 1
  • Severe infection requiring hospitalization 1
  • Age <2 years (not applicable here, but part of the algorithm) 1

For Group A Streptococcal Pharyngitis

• 50-75 mg/kg/day divided into 2 doses for 10 days (approximately 1100-1650 mg twice daily), not exceeding 1000 mg per dose 3, 1
• This translates to approximately 14-21 mL of 400mg/5mL suspension twice daily 3

Critical Dosing Considerations

Maximum daily dose: The FDA label specifies that amoxicillin should not exceed 4000 mg/day regardless of weight 1, 2. For this 44.5 kg child, even the high-dose regimen (4005 mg/day calculated) remains at the maximum threshold.

Common pitfall: Research demonstrates that larger children frequently receive inadequate dosing because clinicians are reluctant to exceed "adult doses" 4. Children above 60 kg are often dosed at less than 40 mg/kg/day, which is subtherapeutic for infections requiring high-dose therapy 4. Do not underdose this patient simply because the calculated dose approaches adult maximum doses.

Treatment Duration and Monitoring

• Duration: Continue treatment for a minimum of 48-72 hours beyond symptom resolution 2
• For Streptococcus pyogenes infections, treat for at least 10 days to prevent acute rheumatic fever 2
• Expected response: Clinical improvement should occur within 48-72 hours; if no improvement or worsening occurs, reevaluate the diagnosis and consider alternative pathogens or complications 1

Administration Instructions

• Administer at the start of meals to minimize gastrointestinal intolerance 2
• Shake oral suspension well before each use 2
• Refrigeration is preferable but not required; discard unused suspension after 14 days 2

When to Use Amoxicillin-Clavulanate Instead

Switch to amoxicillin-clavulanate (Augmentin) 90 mg/kg/day of amoxicillin component if: 1

• β-lactamase-producing organisms suspected (H. influenzae, M. catarrhalis) 1
• Recent antibiotic use within 4-6 weeks 5
• Treatment failure on standard amoxicillin 5