Amoxicillin Dosing for Adults with Bacterial Infections
For adults with bacterial infections, amoxicillin dosing ranges from 500 mg every 12 hours to 875 mg every 12 hours (or 500 mg every 8 hours) depending on infection severity and site, with treatment duration typically 7-10 days for respiratory infections and at least 10 days for streptococcal infections. 1
Standard Dosing by Infection Type and Severity
Mild to Moderate Infections
- Ear/Nose/Throat, Skin, and Genitourinary Tract: 500 mg every 12 hours or 250 mg every 8 hours 1
- Community-Acquired Pneumonia (no comorbidities): 1000 mg every 8 hours 2
- Acute Bacterial Rhinosinusitis (no risk factors): 1.5-4 grams per day divided into doses for 5-7 days 3, 2
Severe Infections
- Ear/Nose/Throat, Skin, and Genitourinary Tract: 875 mg every 12 hours or 500 mg every 8 hours 1
- Lower Respiratory Tract (all severities): 875 mg every 12 hours or 500 mg every 8 hours 1
When to Switch to Amoxicillin-Clavulanate
If the patient has risk factors for resistant pathogens, switch to amoxicillin-clavulanate rather than increasing amoxicillin dose alone. 2 Risk factors include:
- Recent antimicrobial use within 4-6 weeks 3
- Frequent exposure to children in daycare 3
- Immunodeficiency 3
- Age ≥65 years 3
- Nursing home residence 3
- Areas with high prevalence of penicillin-resistant S. pneumoniae 3
For these patients, use amoxicillin-clavulanate 875/125 mg twice daily or the high-dose regimen of 2000/125 mg twice daily 4, 5
Treatment Duration by Infection Type
- Streptococcal infections: Minimum 10 days to prevent acute rheumatic fever 1
- Respiratory tract infections: 7-10 days 4
- Acute bacterial rhinosinusitis: 5-7 days for adults 4, 5
- H. pylori eradication: 14 days (triple therapy: 1 gram twice daily with clarithromycin and lansoprazole; dual therapy: 1 gram three times daily with lansoprazole) 1
- Continue treatment 48-72 hours beyond symptom resolution or bacterial eradication 1
Special Populations
Renal Impairment
- 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: 500 mg or 250 mg every 24 hours, with additional dose during and at end of dialysis 1
- Do NOT use 875 mg dose if GFR <30 mL/min 1
Administration Considerations
Take amoxicillin at the start of a meal to minimize gastrointestinal intolerance. 1 This is particularly important as diarrhea is the most common adverse reaction (>1% incidence) 1
Critical Pitfalls to Avoid
- Do not underdose in severe infections: Lower respiratory tract infections require 875 mg every 12 hours regardless of severity 1
- Do not use amoxicillin alone for β-lactamase producers: H. influenzae and M. catarrhalis often produce β-lactamase; switch to amoxicillin-clavulanate if these pathogens are suspected 3, 6
- Reassess at 72 hours: If no improvement after 3 days, consider switching antibiotics or reevaluating the diagnosis 3
- Complete the full course: Particularly critical for streptococcal infections to prevent rheumatic fever 1
When Amoxicillin May Not Be Effective
Evidence suggests amoxicillin provides limited benefit in viral lower respiratory tract infections 7. However, patients with combined bacterial and viral infections may benefit from reduced illness deterioration (odds ratio 0.24) 7. For strictly bacterial infections, symptom severity reduction is modest (0.26 points on a 0-6 scale) 7.