Amoxicillin Dosing for 80.8 lb (36.7 kg) 9-Year-Old Female
For this 36.7 kg child who can swallow pills, prescribe amoxicillin 45 mg/kg/day divided into two doses (approximately 825 mg twice daily) for mild to moderate infections, or 90 mg/kg/day divided into two doses (approximately 1650 mg twice daily) for severe infections or areas with high pneumococcal resistance. 1, 2
Weight-Based Calculation
- Patient weight: 80.8 pounds = 36.7 kg
- Standard dose (45 mg/kg/day): 36.7 kg × 45 mg/kg = 1,651.5 mg/day, divided into 825 mg twice daily 1, 2
- High dose (90 mg/kg/day): 36.7 kg × 90 mg/kg = 3,303 mg/day, divided into 1,650 mg twice daily 1, 2
Indication-Specific Dosing
Respiratory Tract Infections (Pneumonia, Bronchitis)
- Mild to moderate: 45 mg/kg/day in 2 doses = 825 mg twice daily 1, 3
- Severe or high resistance areas: 90 mg/kg/day in 2 doses = 1,650 mg twice daily 1, 2
- Duration: 10 days for pneumonia; 7-10 days for other respiratory infections 1
Streptococcal Pharyngitis (Strep Throat)
- Dose: 50-75 mg/kg/day in 2 doses = 920-1,375 mg twice daily 1, 2
- Duration: 10 days to prevent acute rheumatic fever 3
Acute Otitis Media (Ear Infection)
- Standard: 40-45 mg/kg/day in 2 doses = 735-825 mg twice daily 2
- Recent antibiotic use (within 4-6 weeks): Consider amoxicillin-clavulanate 90 mg/kg/day instead 1
- Duration: 5-10 days 2
Skin and Soft Tissue Infections
- Mild to moderate: 25 mg/kg/day in 2 doses = 460 mg twice daily 3
- Severe: 45 mg/kg/day in 2 doses = 825 mg twice daily 3
Practical Administration
- Formulation: Since the patient can swallow pills, use 500 mg or 875 mg tablets 3
- Timing: Administer at the start of meals to minimize gastrointestinal side effects 3
- For 825 mg dose: Give one 875 mg tablet twice daily (closest available strength) 3
- For 1,650 mg dose: Give two 875 mg tablets twice daily 3
Critical Monitoring Points
- Clinical improvement should occur within 48-72 hours of starting therapy 4, 1
- If no improvement by 48-72 hours: Reevaluate for treatment failure, consider atypical pathogens, or assess for complications 4, 1
- Complete the full course even if symptoms resolve earlier to prevent resistance and recurrence 1
Important Caveats
High-dose regimen (90 mg/kg/day) is specifically indicated for: 1, 2
- Severe infections
- Areas with high pneumococcal resistance
- Recent antibiotic exposure within past 3 months
- Treatment failure with standard dosing
Common pitfall: Underdosing due to outdated weight-based calculations can lead to treatment failure and promote antimicrobial resistance 2. The recommended doses have increased over time due to rising pneumococcal resistance 2.
Adverse effects to counsel about: 1
- Gastrointestinal disturbances (diarrhea, nausea) are most common
- Rash or hypersensitivity reactions may occur
- Taking with food improves tolerability