Amoxicillin Dosing for Adult Bacterial Infections
For most adult bacterial infections, amoxicillin should be dosed at 500 mg three times daily for mild infections, or 875 mg twice daily for moderate-to-severe respiratory infections, with treatment duration of 7-14 days depending on the infection site. 1
Standard Dosing Regimens by Infection Type
Respiratory Tract Infections
For community-acquired pneumonia and acute bacterial rhinosinusitis, use 875 mg twice daily for 7-10 days. 2, 3 This twice-daily regimen is equally effective as 500 mg three times daily but offers better compliance. 4
- Mild disease without recent antibiotic use (past 4-6 weeks): Start with 1.5 g/day total (500 mg three times daily) 2
- Moderate disease or recent antibiotic exposure: Escalate to 4 g/day total (1 gram three times daily or use amoxicillin-clavulanate) 2
- Duration: 7-10 days for pneumonia 2, 5-7 days for uncomplicated sinusitis 5, 3
Urinary Tract Infections
For uncomplicated UTIs, use 250 mg three times daily for 7 days for bladder infections, or 500 mg three times daily for 14 days for suspected renal infections. 6
- Treatment duration: 3-7 days for uncomplicated cases 5
- Higher doses (500 mg three times daily) are needed when renal involvement is suspected 6
Skin and Soft Tissue Infections
Use 500 mg three times daily or 875 mg twice daily for standard skin infections. 3, 1
- Duration typically 7-10 days based on clinical response 1
Critical Dosing Considerations for Resistant Organisms
When to Use High-Dose Regimens
Increase to 4 g/day (1 gram three times daily) when any of these risk factors are present: 2
- Recent antibiotic use within 4-6 weeks
- Age >65 years
- Frequent exposure to children in daycare
- Immunodeficiency or immunosuppression
- Geographic areas with high prevalence of penicillin-resistant Streptococcus pneumoniae (MIC >2 mg/L)
- Moderate-to-severe disease presentation
- Prior treatment failure
Amoxicillin-Clavulanate Considerations
When adding clavulanate for beta-lactamase-producing organisms, use 875 mg/125 mg twice daily for standard infections, or 2000 mg/125 mg twice daily for drug-resistant pathogens. 5, 3, 7
- The high-dose formulation (2000 mg/125 mg twice daily) achieves adequate serum concentrations against penicillin-resistant S. pneumoniae with MICs up to 4-8 mg/L 5, 7
- Never substitute two 250 mg tablets for one 500 mg tablet, as this results in excessive clavulanate dosing and increased gastrointestinal side effects 3
Renal Dose Adjustments
Reduce dosing frequency in severe renal impairment (GFR <30 mL/min). 1
- Specific adjustments should be based on creatinine clearance
- Maintain adequate dosing intervals to preserve pharmacodynamic targets
Treatment Duration by Indication
- Acute bacterial rhinosinusitis: 5-7 days in adults 5, 3, 10-14 days in children 5
- Community-acquired pneumonia: 7-10 days 2
- Acute exacerbations of chronic bronchitis: 7-10 days 3
- Uncomplicated UTI: 3-7 days 5
- Group A streptococcal pharyngitis: 10 days (though penicillin V is preferred first-line) 3
- H. pylori eradication: 14 days as part of triple or dual therapy 1
Monitoring and Treatment Failure
Reassess clinical response at 48-72 hours. 2, 5
- Lack of improvement or worsening symptoms warrants either:
Common Pitfalls to Avoid
- Underdosing in high-resistance areas: Standard doses may fail against penicillin-resistant S. pneumoniae; use 4 g/day total dose 2, 5
- Inadequate treatment duration: Premature discontinuation increases relapse risk, particularly in respiratory infections 2, 3
- Ignoring recent antibiotic exposure: This is the strongest predictor of resistant organisms and mandates higher doses or alternative agents 2
- Using amoxicillin for atypical pathogens: Amoxicillin lacks activity against Mycoplasma and Chlamydia pneumoniae; add a macrolide or use a fluoroquinolone instead 2