What is the preferred medication for a 73-year-old patient with a Urinary Tract Infection (UTI) caused by Escherichia coli (E. coli), normal Glomerular Filtration Rate (GFR) and normal liver function tests?

Treatment of E. coli UTI in a 73-Year-Old with Normal Renal and Liver Function

For a 73-year-old patient with E. coli UTI and normal renal and liver function, fosfomycin 3g as a single oral dose is the preferred first-line treatment due to its excellent efficacy against E. coli, convenient single-dose administration, and favorable safety profile. 1

First-Line Treatment Options

1. Fosfomycin (3g single oral dose)

   • FDA-approved specifically for uncomplicated UTIs caused by E. coli 1
   • Excellent efficacy against E. coli with minimal resistance concerns
   • Single-dose administration improves compliance
   • Particularly suitable for elderly patients due to minimal drug interactions

2. Nitrofurantoin (100mg twice daily for 5 days)

   • Effective for lower UTIs caused by E. coli
   • Low resistance rates
   • Safe in patients with normal renal function 2
   • Avoid if GFR <30 mL/min

3. Trimethoprim-sulfamethoxazole (160/800mg twice daily for 3 days)

   • Effective against susceptible E. coli strains 3
   • Consider only if local resistance rates are <20%
   • Higher risk of adverse effects in elderly patients

Treatment Algorithm

1. Assess UTI severity and patient factors:

   • Confirm symptomatic UTI (not asymptomatic bacteriuria)
   • Verify normal renal function (GFR) and liver function
   • Check for drug allergies and medication interactions

2. Select antimicrobial therapy:

   • First choice: Fosfomycin 3g single dose
   • Alternative if fosfomycin unavailable: Nitrofurantoin 100mg twice daily for 5 days
   • If both unavailable or contraindicated: Trimethoprim-sulfamethoxazole 160/800mg twice daily for 3 days

3. If patient has risk factors for resistant organisms:

   • Recent antibiotic exposure
   • Healthcare-associated infection
   • Prior UTIs with resistant organisms
   • Consider obtaining culture results before initiating therapy

Special Considerations for Elderly Patients

• UTI diagnosis in older adults requires careful assessment as presentations may be atypical (confusion, functional decline) 2
• Avoid fluoroquinolones in elderly patients unless benefits clearly outweigh risks 2
• Ensure adequate hydration (1500-2000 mL/day if not contraindicated) 2
• Monitor renal function during treatment, especially with potentially nephrotoxic agents

Monitoring and Follow-up

• Assess clinical response within 48-72 hours
• If symptoms persist, reevaluate diagnosis and consider urine culture and susceptibility testing
• Consider imaging to rule out complications if symptoms persist despite appropriate therapy
• No follow-up urine cultures needed if symptoms resolve completely

Pitfalls to Avoid

1. Treating asymptomatic bacteriuria: The IDSA recommends against treating asymptomatic bacteriuria in elderly patients due to risk of antibiotic resistance without mortality benefit 2

2. Overuse of fluoroquinolones: Despite effectiveness against E. coli, fluoroquinolones should be avoided in elderly patients due to increased risk of tendinopathy, CNS effects, and C. difficile infection 2

3. Inappropriate use of carbapenems: While effective against resistant organisms, carbapenems should be reserved for documented multidrug-resistant infections to prevent antimicrobial resistance 4

4. Neglecting renal function: Even with normal baseline renal function, elderly patients are at higher risk for acute kidney injury during infection and treatment

5. Inadequate duration of therapy: Shorter courses are generally preferred to minimize adverse effects and resistance development, but ensure complete symptom resolution