What is the recommended dosage of amoxicillin (amoxicillin) for treating urinary tract infections (UTIs) in adults?

Amoxicillin Dosage for UTI Treatment in Adults

For uncomplicated UTIs caused by susceptible organisms, amoxicillin 500 mg orally every 8 hours for 7 days is the recommended first-line regimen. 1, 2

Standard Dosing Regimens

Uncomplicated UTI (Cystitis)

• Amoxicillin 500 mg orally every 8 hours for 7 days is the standard regimen for uncomplicated urinary tract infections caused by susceptible Enterococcus faecalis and other β-lactamase-negative organisms 1, 2
• This achieves clinical cure rates of 88.1% and microbiological eradication rates of 86% 1
• Alternative dosing: 250 mg every 8 hours for mild infections 2

Complicated UTI or Pyelonephritis

• Amoxicillin 875 mg orally every 12 hours or 500 mg every 8 hours for more severe infections 2
• Duration: 7-14 days depending on clinical response and severity 3, 1
• For catheter-associated UTI with prompt symptom resolution: 7 days is adequate 3
• For delayed response in catheter-associated UTI: extend to 10-14 days 3

High-Dose Regimens for Resistant Organisms

• Amoxicillin 500 mg IV/PO every 8 hours for vancomycin-resistant enterococcus (VRE) UTI, but only when susceptibility is confirmed 3, 1
• High-dose ampicillin (18-30 g IV daily in divided doses) may be used for severe VRE infections 3

Critical Pre-Treatment Considerations

Always obtain urine culture and susceptibility testing before initiating amoxicillin for UTI. 1 This is essential because:

• Approximately 60% of E. faecium and 2% of E. faecalis are vancomycin-resistant with variable ampicillin susceptibility 1
• Amoxicillin is only effective against β-lactamase-negative organisms 2
• Resistance patterns vary significantly by region and patient population 1

When Amoxicillin Should NOT Be Used

Empiric Therapy Limitations

• Do not use amoxicillin empirically for UTI without culture confirmation of susceptibility 1
• Avoid in patients with β-lactamase-producing organisms (requires amoxicillin-clavulanate instead) 2, 4
• Not appropriate for E. coli or Proteus mirabilis unless confirmed susceptible 2

Alternative Agents for Resistant Organisms

For VRE with uncomplicated UTI when amoxicillin resistance is present:

• Fosfomycin 3 g as a single oral dose 3, 1
• Nitrofurantoin 100 mg orally every 6 hours for 7 days 3, 1

For VRE with bacteremia or complicated infection:

• Linezolid 600 mg IV or PO every 12 hours 3, 1
• High-dose daptomycin 8-12 mg/kg/day 3

Duration of Therapy Guidelines

Standard Durations

• Uncomplicated UTI: 7 days for most patients with prompt symptom resolution 3, 1
• Complicated UTI: 7-14 days depending on clinical response 3, 1
• Catheter-associated UTI: 7 days if symptoms resolve promptly; 10-14 days if delayed response 3

Shorter Courses (Selected Patients Only)

• 3-day regimen: May be considered for women ≤65 years with uncomplicated UTI after catheter removal 3
• Single-dose therapy (3 g) has lower cure rates (60.6% vs 73.6% for 14-day therapy) and is not recommended for routine use 5

Extended Therapy Indications

• 7-14 days: For uncomplicated cases with associated bacteremia 1
• Beyond 14 days: Patients with signs of endocarditis, persistent bacteremia >72 hours, or metastatic infection require extended therapy and specialist consultation 1

Common Pitfalls to Avoid

Do not extend treatment beyond 7 days for uncomplicated UTI without clear indication, as this increases antibiotic resistance risk without proven benefit. 1 Key mistakes include:

• Using amoxicillin empirically without culture confirmation 1
• Failing to adjust therapy based on susceptibility results 2
• Treating asymptomatic bacteriuria (especially in catheterized patients) 3
• Using fluoroquinolones for enterococcal UTI (46-47% resistance rates) 1
• Prescribing moxifloxacin for UTI (inadequate urinary concentrations) 3

Administration Recommendations

• Take at the start of a meal to minimize gastrointestinal intolerance 2
• Continue treatment for minimum 48-72 hours beyond symptom resolution 2
• For Streptococcus pyogenes infections: minimum 10 days to prevent acute rheumatic fever 2

Renal Dose Adjustments

For patients with severe renal impairment:

• GFR 10-30 mL/min: 500 mg or 250 mg every 12 hours 2
• GFR <10 mL/min: 500 mg or 250 mg every 24 hours 2
• Hemodialysis: 500 mg or 250 mg every 24 hours, with additional dose during and at end of dialysis 2
• Do NOT use 875 mg dose in patients with GFR <30 mL/min 2