Amoxicillin Dosing for Uncomplicated UTI
For uncomplicated UTI in adults, amoxicillin 500 mg orally every 8 hours for 7 days is the recommended dose, though amoxicillin is not a first-line agent for typical UTIs due to high E. coli resistance rates. 1
When Amoxicillin is Appropriate
Enterococcal UTIs (Primary Indication)
- Amoxicillin 500 mg orally every 8 hours is first-line therapy for uncomplicated pansensitive Enterococcus faecalis UTIs 1
- This achieves high clinical (88.1%) and microbiological (86%) eradication rates 1
- Treatment duration: 7 days 1
Alternative: Amoxicillin-Clavulanate
- For broader coverage when amoxicillin alone is insufficient, use amoxicillin-clavulanate 250-500 mg every 8 hours 2
- This combination addresses beta-lactamase producing organisms 2
- Microbiological cure rates: 84% at 1 week, 67% at 1 month for recurrent UTIs 2
Pediatric Dosing (Ages 2-24 Months)
- Amoxicillin-clavulanate 20-40 mg/kg per day divided into 3 doses 3
- Treatment duration: 7-14 days 3
- Maximum dose: 4000 mg/day 3
Critical Limitations
Why Amoxicillin is NOT First-Line for Typical UTIs
- E. coli (the most common uropathogen) frequently demonstrates amoxicillin resistance 4, 5
- Cure rates for unselected UTIs are only 60-74% with amoxicillin monotherapy 5, 6
- Immediate treatment failures occur when amoxicillin-resistant pathogens are present 6
Preferred First-Line Agents for Typical UTIs
- Nitrofurantoin, trimethoprim-sulfamethoxazole, or fosfomycin are superior choices for empiric therapy of uncomplicated cystitis caused by E. coli 3, 1
- Reserve amoxicillin for culture-proven susceptible organisms, particularly Enterococcus species 1
Alternative Dosing Regimens
Single-Dose Therapy (Historical, Not Recommended)
- Single 3 g dose achieved only 60.6% cure rates versus 73.6% for 14-day therapy 5
- Higher failure rates in patients with upper tract involvement 7
- Not recommended for current practice due to inferior efficacy 5
Standard Multi-Day Regimens
- 250 mg three times daily for 7 days for lower UTI 6
- 500 mg three times daily for 14 days for suspected pyelonephritis 6
- The 500 mg dose is preferred for more reliable tissue penetration 6
Important Caveats
- Always obtain culture and susceptibility testing before using amoxicillin for UTI 1, 6
- Amoxicillin significantly alters periurethral flora, with 68% of patients acquiring resistant organisms or Candida 6
- Avoid in areas with high E. coli resistance rates (>20%) 4, 6
- Side effects are generally mild (20% incidence) and rarely require discontinuation 2