What antibiotic (ABx) should be prescribed for a 71-year-old female with Escherichia coli (E. coli) urinary tract infection (UTI)?

Antibiotic Treatment for E. coli UTI in a 71-Year-Old Female

For a 71-year-old female with E. coli urinary tract infection (100K colony count), nitrofurantoin or fosfomycin should be prescribed as first-line therapy due to their continued effectiveness against E. coli and low resistance rates. 1, 2

First-Line Treatment Options

• Nitrofurantoin (100mg twice daily for 5 days)

  • Maintains low resistance rates against E. coli
  • Appropriate for uncomplicated lower UTIs
  • Contraindicated if CrCl <30 mL/min

• Fosfomycin (3g single dose)

  • Single-dose treatment improves compliance
  • Effective against most E. coli strains including some resistant strains
  • Well-tolerated in elderly patients

Second-Line Treatment Options

If first-line options are contraindicated:

• Amoxicillin-clavulanate (500/125mg twice daily for 5-7 days)

  • Consider local resistance patterns (ranges from 5.3% to 37.6% in European countries) 2
  • Appropriate for uncomplicated UTIs when first-line agents cannot be used

• Cephalexin (500mg twice daily for 5-7 days)

  • Alternative for patients with contraindications to first-line agents
  • Monitor for allergic cross-reactivity in penicillin-allergic patients

Avoid Fluoroquinolones

• Ciprofloxacin and other fluoroquinolones should be avoided as first-line therapy despite FDA approval for E. coli UTIs 3
• Risk factors for ciprofloxacin resistance include:
  • Advanced age (OR 1.03) 4
  • Prior fluoroquinolone use (OR 2.24) 5
  • Recurrent UTIs (OR 2.26) 5
  • Prior urinary catheterization (OR 2.41) 5

Special Considerations for Elderly Patients

• Assess renal function before prescribing nitrofurantoin
• Consider drug interactions with other medications common in elderly patients
• Evaluate for complicated UTI factors (structural abnormalities, diabetes, immunosuppression) 6
• For postmenopausal women, consider topical vaginal estrogen for prevention of recurrent UTIs 6, 7

Treatment Duration

• Uncomplicated UTI: 3-5 days of therapy 7
• Complicated UTI: 7-14 days of therapy 7

Monitoring and Follow-up

• Obtain culture before starting antibiotics if:
  • Suspected resistant infection
  • Recurrent UTIs (≥3 episodes in 12 months) 6
  • Local E. coli resistance to common antibiotics exceeds 10-20% 7
• Reassess therapy at 48-72 hours based on culture results and clinical response

Prevention of Recurrence

For patients with recurrent UTIs:

• Increased fluid intake
• Urge-initiated and post-coital voiding
• Topical vaginal estrogen for postmenopausal women 6, 7
• Consider methenamine hippurate as an alternative to prophylactic antibiotics 6

Common Pitfalls to Avoid

• Using trimethoprim-sulfamethoxazole empirically without susceptibility data (resistance rates 14.6-60% in Europe) 2
• Prescribing fluoroquinolones as first-line therapy (increasing resistance rates and risk of adverse effects) 2, 5
• Treating asymptomatic bacteriuria in elderly patients (increases risk of resistant infections) 7
• Failing to adjust dosing based on renal function in elderly patients

By following these evidence-based recommendations, you can effectively treat E. coli UTI in this 71-year-old female while minimizing the risk of treatment failure and antibiotic resistance.