Amoxicillin Dosing
For most common infections in children and adults, amoxicillin should be dosed at 40-90 mg/kg/day divided into 2-3 doses, with specific dosing determined by infection severity and site.
Pediatric Dosing (Children ≥3 months and <40 kg)
Standard Dosing by Infection Severity 1
Mild to Moderate Infections (Ear/Nose/Throat, Skin, Genitourinary):
- 25 mg/kg/day divided every 12 hours OR
- 20 mg/kg/day divided every 8 hours
Severe Infections (Lower respiratory tract, severe ENT/skin infections):
- 45 mg/kg/day divided every 12 hours OR
- 40 mg/kg/day divided every 8 hours
Specific Clinical Scenarios
Community-Acquired Pneumonia:
- 50-75 mg/kg/day in 2 doses for uncomplicated cases 2
- Higher doses (75-100 mg/kg/day) if β-lactamase negative H. influenzae suspected 2
- Duration: 5-10 days depending on severity 3, 4
Streptococcal Pharyngitis:
- 50 mg/kg once daily (maximum 1000 mg) for 10 days 5
- Alternative: 25 mg/kg twice daily (maximum 500 mg per dose) 5
Impetigo/Skin Infections:
- 25 mg/kg/day in 3-4 divided doses 6
Neonates and Infants <3 Months 1
Maximum dose: 30 mg/kg/day divided every 12 hours due to immature renal function. This is a critical ceiling that should not be exceeded in this age group.
Adult Dosing
Standard Infections 1
Mild to Moderate Infections:
- 500 mg every 12 hours OR
- 250 mg every 8 hours
Severe Infections:
- 875 mg every 12 hours OR
- 500 mg every 8 hours
Helicobacter pylori Eradication 1
Triple Therapy:
- 1 gram amoxicillin twice daily (every 12 hours) + clarithromycin 500 mg + lansoprazole 30 mg for 14 days
Dual Therapy:
- 1 gram amoxicillin three times daily (every 8 hours) + lansoprazole 30 mg for 14 days
Critical Dosing Considerations
The Weight-Based Dosing Disparity
A significant clinical problem exists: Children >60 kg frequently receive inadequate doses when providers cap amoxicillin at "adult maximum doses" 7, 8. Research demonstrates that larger children systematically receive <40 mg/kg/day when they should receive 80-90 mg/kg/day for resistant organisms. Do not artificially cap doses at adult maximums for children who require weight-based dosing for adequate coverage.
Renal Impairment 1
GFR 10-30 mL/min:
- 500 mg or 250 mg every 12 hours (depending on severity)
GFR <10 mL/min:
- 500 mg or 250 mg every 24 hours
Hemodialysis:
- 500 mg or 250 mg every 24 hours
- Additional dose during and at end of dialysis
Important: Patients with GFR <30 mL/min should NOT receive the 875 mg dose 1.
Duration of Therapy
Streptococcal infections: Minimum 10 days to prevent acute rheumatic fever 1, 9
Pneumonia:
- 5 days for uncomplicated cases showing early improvement 3, 4
- 7-10 days for more severe presentations 2
General principle: Continue 48-72 hours beyond symptom resolution or bacterial eradication 1
Administration Guidelines
- Take at the start of meals to minimize gastrointestinal intolerance 1
- Oral suspension must be shaken well before each use 1
- Reconstituted suspension expires after 14 days; refrigeration preferred but not required 1
Common Pitfalls to Avoid
Underdosing larger children by capping at adult doses when weight-based dosing indicates higher amounts are needed 7, 8
Using first-generation cephalosporins (like cephalexin) as substitutes—these are inactive against many organisms requiring amoxicillin 9
Prescribing 875 mg tablets to patients with GFR <30 mL/min 1
Stopping therapy too early in streptococcal infections—must complete full 10-day course 1
Forgetting the twice-daily option in children, which improves adherence compared to three-times-daily dosing 5, 10