What is the recommended antibiotic treatment for a urinary tract infection (UTI) caused by Escherichia coli (E. coli)?

Antibiotic Treatment for E. coli Urinary Tract Infections

For uncomplicated cystitis in women, use nitrofurantoin 100 mg twice daily for 5 days, fosfomycin 3g single dose, or amoxicillin-clavulanate as first-line therapy; for pyelonephritis, use ceftriaxone 1-2g IV/IM daily if ciprofloxacin resistance exceeds 10% or the patient used fluoroquinolones within 6 months. 1, 2

Uncomplicated Lower UTI (Acute Cystitis)

First-line options:

• Nitrofurantoin 100 mg orally twice daily for 5 days - maintains 83.2% sensitivity against E. coli including ESBL-producing strains 1, 3
• Fosfomycin 3g single oral dose - FDA-approved specifically for uncomplicated cystitis caused by E. coli 4, 1
• Amoxicillin-clavulanate - recommended by WHO with high susceptibility rates in urinary E. coli isolates 1, 2

Second-line options when first-line agents are contraindicated:

• Trimethoprim-sulfamethoxazole for 5 days - only use if local resistance is documented <20%; many communities now exceed this threshold 1, 2, 5

Critical error to avoid: Never use amoxicillin alone - resistance rates reach 75% in E. coli 1

Pyelonephritis (Mild to Moderate)

Decision algorithm for empiric therapy:

If ALL of the following criteria are met, use ciprofloxacin:

• Local fluoroquinolone resistance <10% 1, 2
• No fluoroquinolone use in past 6 months 1
• Outpatient oral treatment feasible 1
• Patient not from urology department 1

Otherwise, use ceftriaxone 1-2g IV/IM once daily - this is the preferred option per American College of Physicians 1, 2

Alternative: Cefotaxime IV - equivalent efficacy to ceftriaxone 1

Duration: 7-14 days depending on clinical response; premature discontinuation leads to recurrence 1, 2

Severe Pyelonephritis or Complicated UTI

First-line parenteral therapy:

• Ceftriaxone 1-2g IV/IM daily 1, 2
• Cefotaxime IV 1

Second-line option:

• Amikacin - preferred over gentamicin because it maintains superior activity against ESBL-producing E. coli 1, 2, 6
• Dose: 15 mg/kg/day intramuscularly for 10 days 6
• Clinical success rate 97.2%, bacteriological success 94.1% 6

Critical error to avoid: Do not use aminoglycosides as monotherapy without documented susceptibility 1

Extended-Spectrum Beta-Lactamase (ESBL) Producing E. coli

For uncomplicated cystitis:

• Nitrofurantoin - maintains 83.2% sensitivity 1
• Fosfomycin 3g single dose 3
• Amoxicillin-clavulanate (for ESBL E. coli only, not Klebsiella) 3

For complicated UTI/pyelonephritis:

• Carbapenems (meropenem, imipenem) - gold standard for severe infections 3
• Piperacillin-tazobactam - acceptable for ESBL E. coli if susceptible 3
• Amikacin 15 mg/kg/day - highly effective with 94% bacteriological cure rate 6

Critical error to avoid: Never assume ceftriaxone efficacy against ESBL strains without susceptibility testing 1

Carbapenem-Resistant E. coli (CRE)

For uncomplicated cystitis:

• Gentamicin or amikacin single dose - requires intravenous administration 1

For complicated UTI/pyelonephritis:

• Ceftazidime-avibactam 2, 3
• Meropenem-vaborbactam 2, 3
• Imipenem-cilastatin-relebactam 2, 3
• Plazomicin 15 mg/kg IV every 12 hours 2

Recurrent UTI Considerations

Definition: Three or more symptomatic infections within 12 months 7

E. coli causes 75% of recurrent UTIs 7

Before considering antibiotic prophylaxis, implement behavioral measures:

• Adequate hydration for frequent urination 7
• Post-coital voiding 7
• Avoid spermicidal contraceptives 7
• Topical vaginal estrogens for postmenopausal women with atrophic vaginitis 7

Imaging is NOT routinely indicated unless bacterial persistence occurs (recurrence within 2 weeks) or patient has risk factors for complicated UTI 7

Key Resistance Patterns to Remember

• Trimethoprim-sulfamethoxazole: Resistance exceeds 20% in many communities; verify local susceptibility before empiric use 1, 2, 5
• Ciprofloxacin: Increasing resistance precludes first-line use for uncomplicated cystitis; reserve for pyelonephritis only when resistance <10% 1, 2, 3
• Amoxicillin monotherapy: 75% resistance - never use 1

Special Populations

Pregnancy: Ciprofloxacin should not be used unless potential benefit justifies risk; no evidence of teratogenicity but insufficient safety data 8

Pediatric patients: Ciprofloxacin is indicated for complicated UTI and pyelonephritis in children but is not first-choice due to increased joint-related adverse events (9.3% vs 6% for controls) 8

Elderly patients: Increased risk of tendon rupture with fluoroquinolones, especially with concurrent corticosteroid use 8