What is the antibiotic of choice for Escherichia coli (E. coli) infections?

Antibiotic Treatment for Escherichia coli Infections

For E. coli infections, the first-line antibiotic choice is ciprofloxacin when the organism is susceptible, particularly for systemic infections such as bacteremia. 1

First-Line Options Based on Infection Site

Systemic Infections (Bacteremia/Septicemia)

• Intravenous therapy is typically initiated with:
  • Ceftriaxone 1-2g IV daily 2
  • Piperacillin/tazobactam or third-generation cephalosporins for more severe cases 3
• Oral step-down therapy (when clinically stable):
  • Ciprofloxacin 500mg twice daily (preferred oral option) 1, 4
  • TMP-SMX 160/800mg twice daily (alternative if fluoroquinolone contraindicated) 1

Urinary Tract Infections

• For uncomplicated UTIs:
  • Ciprofloxacin 250-500mg twice daily 4
  • Amoxicillin-clavulanate for susceptible strains 5
  • TMP-SMX 160/800mg twice daily 1
• For complicated UTIs:
  • Initial IV therapy with ceftriaxone 2
  • Step down to oral therapy based on susceptibility 3

Intra-abdominal Infections

• Often polymicrobial, requiring broader coverage:
  • Piperacillin/tazobactam (sufficient anaerobic coverage) 3
  • Third-generation cephalosporins with anaerobic coverage 3
  • For oral step-down, ciprofloxacin plus metronidazole 3

Special Considerations

Antimicrobial Resistance

• Local antibiogram and susceptibility patterns should guide therapy 2
• For multidrug-resistant E. coli:
  • Consider carbapenems or newer agents like ceftazidime/avibactam 3
  • Extended-spectrum penicillins (e.g., piperacillin/tazobactam) or extended-spectrum cephalosporins may be needed 3

Biliary Infections

• E. coli is a common cause of biliary infections 3
• First-line for mild episodes: oral aminopenicillin/beta-lactamase inhibitor 3
• For severe cases: IV piperacillin/tazobactam or third-generation cephalosporins 3
• Fluoroquinolones should be reserved for specific cases due to resistance concerns 3

Duration of Therapy

• Uncomplicated UTI: 3-7 days 3
• Complicated UTI: 5-7 days 3
• Bacteremia: 7-14 days 3
• Intra-abdominal infections: 5-7 days 3

Important Caveats

• Avoid fluoroquinolones in pediatric patients due to increased risk of adverse events related to joints/surrounding tissues 4
• For E. coli O157:H7 causing bloody diarrhea, antibiotics should be avoided due to increased risk of hemolytic uremic syndrome 6, 7
• In cases of severe sepsis, combination therapy may be considered initially until susceptibilities are known 3
• When treating biliary infections, biliary decompression may be necessary in addition to antibiotics for high-grade strictures 3

Algorithm for Antibiotic Selection for E. coli

1. Determine infection site and severity
2. Check local antibiogram and patient's previous cultures if available
3. For severe/systemic infection: Start IV therapy (ceftriaxone or piperacillin/tazobactam)
4. For non-severe infection: Start oral therapy (ciprofloxacin or TMP-SMX)
5. Adjust therapy based on culture results and clinical response
6. Consider step-down to oral therapy when clinically stable

Remember that increasing resistance to fluoroquinolones is a concern, so these agents should be used judiciously despite being first-line for many E. coli infections 3, 1.