Amoxicillin Dosing and Duration
For most common bacterial infections in adults and children ≥3 months, amoxicillin should be dosed at 500 mg three times daily (or 25 mg/kg/day divided three times daily in children) for 10 days, with higher doses of 875 mg twice daily (or 45 mg/kg/day divided twice daily) reserved for severe infections or resistant organisms. 1
Standard Dosing by Infection Type
Group A Streptococcal Pharyngitis
- Adults: 500 mg twice daily OR 250 mg four times daily for 10 days 2, 3
- Children: 50 mg/kg once daily (max 1000 mg) OR 25 mg/kg twice daily (max 500 mg per dose) for 10 days 2, 3
- Critical point: The 10-day duration is essential to prevent acute rheumatic fever 1
Acute Otitis Media (AOM)
- High-dose amoxicillin is now standard: 80-90 mg/kg/day divided twice daily for children 4
- Adults: 875 mg twice daily
- Duration: Typically 5-10 days depending on age and severity 4
- Rationale: Higher doses overcome penicillin-resistant Streptococcus pneumoniae (though resistance patterns vary geographically) 5, 6, 7
Skin and Soft Tissue Infections
- Mild/Moderate: 500 mg every 12 hours OR 250 mg every 8 hours for adults; 25 mg/kg/day divided every 12 hours for children 8, 9, 1
- Severe: 875 mg every 12 hours OR 500 mg every 8 hours for adults; 45 mg/kg/day divided every 12 hours for children 8, 9, 1
- Duration: 7-14 days 8
Erysipeloid
- Dose: 500 mg three times daily for 7-10 days 8
Community-Acquired Pneumonia (CAP)
- Adults: 875 mg every 12 hours OR 500 mg every 8 hours 1
- Children: 45 mg/kg/day divided every 12 hours OR 40 mg/kg/day divided every 8 hours 1
- Duration: Recent evidence supports 3-5 days for uncomplicated cases achieving clinical stability, rather than traditional 7-10 days 10, 11
- 3 days if clinically stable by day 3
- 5 days if stability achieved by day 5
- 7 days for other uncomplicated cases
Lyme Disease (Early)
- Dose: 500 mg three times daily for adults; 50 mg/kg/day in 3 divided doses (max 500 mg per dose) for children 12
- Duration: Typically 14-21 days 12
H. pylori Eradication
- Triple therapy: 1 gram twice daily with clarithromycin 500 mg and lansoprazole 30 mg for 14 days 1
- Dual therapy: 1 gram three times daily with lansoprazole 30 mg for 14 days 1
Key Clinical Considerations
When to Use Higher Doses
Higher doses (80-90 mg/kg/day in children, 875 mg twice daily in adults) are indicated for:
- Severe infections 1
- Lower respiratory tract infections 1
- Recent antibiotic use within 4-6 weeks 13
- Geographic areas with high penicillin-resistant S. pneumoniae prevalence 4, 5
- Concurrent conjunctivitis with AOM 4
Duration Principles
- Minimum 48-72 hours beyond symptom resolution for most infections 1
- 10 days mandatory for Streptococcus pyogenes (Group A Strep) to prevent rheumatic fever 1
- Shorter courses (3-5 days) increasingly supported for uncomplicated pneumonia when clinical stability achieved 10, 11
- Longer courses (several weeks) may be needed for complicated infections 1
Renal Impairment Adjustments
- GFR 10-30 mL/min: 500 mg or 250 mg every 12 hours 1
- GFR <10 mL/min: 500 mg or 250 mg every 24 hours 1
- Hemodialysis: Additional dose during and after dialysis 1
- Do NOT use 875 mg dose if GFR <30 mL/min 1
Administration Tips
- Take at the start of meals to minimize gastrointestinal intolerance 1
- Suspension remains stable for 14 days after reconstitution (refrigeration preferred but not required) 1
- For children <3 months: Maximum 30 mg/kg/day divided every 12 hours due to immature renal function 1, 14
Common Pitfalls to Avoid
- Underdosing in obesity: While guidelines recommend weight-based dosing, many clinicians cap doses at standard adult maximums even when calculated doses exceed them 6
- Inadequate duration for strep throat: Stopping before 10 days risks rheumatic fever 1
- Using first-generation cephalosporins: These are inactive against many respiratory pathogens and should not substitute for amoxicillin 12
- Ignoring recent antibiotic exposure: Prior use within 4-6 weeks necessitates broader coverage (consider amoxicillin-clavulanate) 13, 4