What is the recommended antibiotic regimen for an Escherichia coli (E. coli) urinary tract infection (UTI)?

Antibiotic Treatment for E. coli Urinary Tract Infections

For uncomplicated E. coli UTIs, first-line treatment options include nitrofurantoin 100 mg twice daily for 5 days, trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days (if local resistance <20%), or fosfomycin 3 g single dose. 1

First-Line Treatment Options

Nitrofurantoin

• Dosage: 100 mg twice daily for 5 days
• Advantages:
  • Minimal resistance patterns
  • Limited collateral damage to gut flora
  • Excellent activity against most E. coli strains
• Contraindications:
  • Avoid in suspected pyelonephritis
  • Avoid if GFR <30 ml/min
  • Avoid in infants less than 4 months 1

Trimethoprim-sulfamethoxazole (TMP-SMX)

• Dosage: 160/800 mg twice daily for 3 days
• Considerations:
  • Only use if local E. coli resistance is <20%
  • Avoid if used for UTI treatment in previous 3 months
  • FDA-approved for E. coli UTIs 2
  • Higher resistance rates in the US (21.3%) compared to Canada 3

Fosfomycin

• Dosage: 3 g single dose
• Advantages:
  • Convenient single-dose regimen
  • FDA approved for E. coli UTIs
  • Active against many resistant strains
• Limitations:
  • Somewhat lower efficacy than other first-line agents
  • Avoid if pyelonephritis is suspected 1

Second-Line Treatment Options

Fluoroquinolones (e.g., Ciprofloxacin)

• Should be reserved as alternative treatment when first-line agents cannot be used
• Concerns include:
  • Promoting resistance
  • Potential association with MRSA
  • Higher resistance rates in patients ≥65 years 1, 3

Oral Cephalosporins

• Options include cephalexin or cefixime
• Consider when first-line agents are contraindicated 4

Amoxicillin-Clavulanate

• Alternative when first-line options cannot be used 4

Treatment for Complicated or Resistant E. coli UTIs

For ESBL-producing E. coli:

• Oral options: nitrofurantoin, fosfomycin, pivmecillinam (if available) 4
• Parenteral options: carbapenems, ceftazidime-avibactam, aminoglycosides 4

For Carbapenem-Resistant E. coli:

• Treatment options include:
  • Ceftazidime-avibactam
  • Meropenem-vaborbactam
  • Imipenem-cilastatin-relebactam
  • Plazomicin 1

Treatment Duration

• Uncomplicated cystitis: 3-5 days
• Complicated UTI or pyelonephritis: 10-14 days 1

Special Considerations

Pregnant Women

• Nitrofurantoin 100 mg twice daily for 5-7 days (if normal renal function) 1

Hemodialysis Patients

• TMP-SMX at half the standard dose, administered after each dialysis session 1

Monitoring and Follow-up

• Assess clinical improvement within 48-72 hours
• Adjust treatment based on culture and susceptibility results when available 1

Common Pitfalls to Avoid

1. Using nitrofurantoin for suspected pyelonephritis (inadequate tissue penetration)
2. Prescribing TMP-SMX empirically in areas with >20% resistance
3. Using fluoroquinolones as first-line therapy (contributes to resistance)
4. Failing to adjust therapy based on culture results
5. Not considering local resistance patterns when selecting empiric therapy

Prevention Strategies

• Increased fluid intake (additional 1.5L daily) may help prevent recurrence
• For recurrent UTIs, consider antibiotic prophylaxis with nitrofurantoin 50-100 mg daily or TMP-SMX 1