What is the recommended dose of amoxicillin (amoxicillin) for treating E. coli (Escherichia coli) infections?

Amoxicillin Dosing for E. coli Infections

For E. coli infections, amoxicillin is generally not recommended as first-line therapy due to high resistance rates (up to 86%), unless susceptibility is confirmed by culture. 1

Treatment Recommendations by Infection Type

Urinary Tract Infections (UTIs)

• Uncomplicated UTIs:

  • Amoxicillin is NOT recommended empirically due to high resistance rates
  • Preferred first-line options:
    • Nitrofurantoin 100mg twice daily for 5 days (96.4% sensitivity) 2, 1
    • Trimethoprim-sulfamethoxazole 160/800mg twice daily for 3 days (if susceptible) 2
    • Fosfomycin 3g single dose 2

• If E. coli is confirmed susceptible to amoxicillin:

  • Amoxicillin 500mg PO every 8 hours for uncomplicated UTIs 3
  • Consider amoxicillin/clavulanate for better coverage 2

Gastrointestinal E. coli Infections

• For enterotoxigenic, enteropathogenic, and enteroinvasive E. coli:

  • TMP-SMX or fluoroquinolones are preferred 3
  • Amoxicillin is not specifically recommended in guidelines

• For enterohemorrhagic E. coli (STEC):

  • Antibiotics should be avoided as they may increase risk of hemolytic uremic syndrome 3

Dosing When Amoxicillin Is Appropriate

When E. coli susceptibility to amoxicillin is confirmed:

1. Standard adult dosing:

   • 500mg orally every 8 hours 3
   • Duration: 3-7 days for uncomplicated UTIs, 7-14 days for complicated infections 2

2. High-dose option (for severe infections):

   • 875mg orally every 8-12 hours 4
   • For severe infections: up to 18-30g IV daily in divided doses 3

3. Combination therapy options:

   • Amoxicillin/clavulanate 875/125mg every 12 hours 2
   • Amoxicillin/sulbactam 875/125mg every 12 hours 4

Important Considerations

• Resistance patterns: Local resistance patterns should guide therapy; E. coli resistance to amoxicillin is high globally (86% in some regions) 1

• Susceptibility testing: Rapid detection of amoxicillin-susceptible E. coli (ASEC) can help limit broad-spectrum antibiotic use 5

• Co-selection of resistance: Amoxicillin use has been associated with increased resistance not only to itself but also to ciprofloxacin 6

• Synergistic effects: Combining amoxicillin with beta-lactamase inhibitors (clavulanate or sulbactam) significantly improves efficacy against resistant strains 4, 7

• Monitoring: Clinical response should be assessed within 72 hours of initiating therapy 2

When to Use Alternative Antibiotics

• If local resistance rates to amoxicillin exceed 20% (which is common for E. coli)
• For empiric therapy before susceptibility results
• When treating severe or complicated infections
• In immunocompromised patients

Amoxicillin alone should only be used for E. coli infections when susceptibility has been confirmed by culture and sensitivity testing, as resistance rates are high worldwide.