Amoxicillin Dosing for Adults
For most adult infections, amoxicillin should be dosed at 500 mg every 8 hours or 875 mg every 12 hours for mild to moderate infections, and 875 mg every 12 hours or 500 mg every 8 hours for severe infections 1.
Standard Dosing by Infection Type
Respiratory Tract Infections
- Mild to moderate: 500 mg every 12 hours OR 250 mg every 8 hours 1
- Severe (including pneumonia): 875 mg every 12 hours OR 500 mg every 8 hours 1
- Community-acquired pneumonia: High-dose amoxicillin 1 g every 8 hours is recommended for outpatients with comorbidities 2
Skin and Soft Tissue Infections
- Mild to moderate: 500 mg every 12 hours OR 250 mg every 8 hours 1
- Severe: 875 mg every 12 hours OR 500 mg every 8 hours 1
- Impetigo: 875/125 mg (amoxicillin-clavulanate) twice daily 3
Acute Bacterial Rhinosinusitis
- High-dose amoxicillin-clavulanate is preferred: 2 g orally twice daily 4
- This higher dose is specifically recommended due to increasing rates of resistant Streptococcus pneumoniae 4
Genitourinary Tract Infections
- Mild to moderate: 500 mg every 12 hours OR 250 mg every 8 hours 1
- Severe: 875 mg every 12 hours OR 500 mg every 8 hours 1
Helicobacter pylori Infection
- Triple therapy: 1 gram amoxicillin twice daily (every 12 hours) for 14 days, combined with clarithromycin 500 mg and lansoprazole 30 mg 1
- Dual therapy: 1 gram amoxicillin three times daily (every 8 hours) for 14 days with lansoprazole 30 mg 1
Animal/Human Bites
- Amoxicillin-clavulanate 875/125 mg twice daily is the preferred oral regimen 3
Special Dosing Considerations
Renal Impairment
Dose adjustments are mandatory for severe renal dysfunction 1:
- GFR 10-30 mL/min: 500 mg or 250 mg every 12 hours
- GFR <10 mL/min: 500 mg or 250 mg every 24 hours
- Hemodialysis: 500 mg or 250 mg every 24 hours, with an additional dose during and at the end of dialysis
Critical caveat: Patients with GFR <30 mL/min should NOT receive the 875 mg dose 1.
Administration Timing
Take amoxicillin at the start of a meal to minimize gastrointestinal intolerance 1. This is an important practical detail often overlooked.
Duration of Treatment
- Minimum duration: Continue for 48-72 hours beyond symptom resolution or evidence of bacterial eradication 1
- Streptococcal infections: Minimum 10 days to prevent acute rheumatic fever 1
- Community-acquired pneumonia: 5-7 days for uncomplicated cases in adults 2
- Acute bacterial sinusitis: 5-7 days for adults 4
- H. pylori: 14 days 1
High-Dose Considerations
Recent evidence supports high-dose amoxicillin in specific scenarios:
- For resistant S. pneumoniae: High-dose formulations (1 g three times daily or 2 g twice daily) maintain adequate serum levels against organisms with MICs up to 4 mg/L 5, 6
- Acute sinusitis: High-dose immediate-release formulations (1750 mg twice daily) showed 18% greater improvement at day 3 compared to standard dosing, though with increased diarrhea risk (15.8% vs 4.8%) 7
- Bacteremia: High-dose oral amoxicillin (1 g three times daily) has shown 92% clinical cure rates when transitioning from IV therapy 8
Common Pitfalls to Avoid
- Don't underdose respiratory infections: For pneumonia with comorbidities, use high-dose regimens (1 g every 8 hours), not standard doses 2
- Don't forget renal adjustment: The 875 mg dose is contraindicated in severe renal impairment 1
- Don't use amoxicillin alone for sinusitis: Amoxicillin-clavulanate is preferred due to beta-lactamase producing organisms 4
- Don't prescribe inadequate duration: Ensure at least 48-72 hours beyond clinical improvement 1