What is the recommended antibiotic treatment for a 91-year-old patient with a resistant urinary tract infection (UTI)?

Antibiotic Treatment for Resistant UTI in a 91-Year-Old Patient

For a 91-year-old patient with a resistant urinary tract infection, intravenous fosfomycin at a dose of 4g every 6 hours is recommended, with the option to step down to oral fosfomycin trometamol 3g every 24-72 hours after clinical improvement. 1

Initial Management Steps

1. Obtain urine culture before starting antibiotics

   • Essential due to wide spectrum of potential infecting organisms and increased likelihood of antimicrobial resistance 2
   • Culture results guide targeted therapy and prevent treatment failure

2. Replace indwelling catheter if present

   • If catheter has been in place for ≥2 weeks, replace it before starting antibiotics 2
   • Obtain urine specimen from the freshly placed catheter
   • Catheter replacement hastens symptom resolution and reduces risk of subsequent bacteriuria and UTI

Antibiotic Selection for Resistant UTIs

First-line options:

• Intravenous fosfomycin (4g q6h) with step-down to oral fosfomycin (3g q24-72h) 1
  • Effective against ESBL-producing and cephalosporin-resistant Enterobacterales
  • Supported by high-quality RCTs (ZEUS and FOREST)
  • Monitor for heart failure (8.6% risk in clinical trials)

Alternative options (based on susceptibility):

• Ceftazidime/avibactam (2.5g IV q8h) 1, 3
• Meropenem/vaborbactam (4g IV q8h) 1, 3
• Imipenem/cilastatin/relebactam (1.25g IV q6h) 1, 3
• Aminoglycosides (for urinary source infections):
  • Gentamicin 5-7 mg/kg/day IV once daily
  • Amikacin 15 mg/kg/day IV once daily 1

Treatment Duration

• 7 days for patients with prompt symptom resolution 2
• 10-14 days for patients with delayed response 2
• Duration applies regardless of whether patient remains catheterized

Special Considerations for Elderly Patients

• Avoid nitrofurantoin in patients with renal impairment (CrCl <60 mL/min), common in elderly patients 1
• Consider renal dosing adjustments for all antibiotics based on estimated GFR
• Monitor closely for adverse effects, which occur more frequently in elderly patients
• Assess for drug interactions with other medications the patient may be taking

Follow-up

• Assess clinical response within 48-72 hours of treatment initiation 1
• Consider follow-up urine culture in complicated cases or treatment failures
• If symptoms persist despite appropriate therapy, evaluate for:
  • Structural abnormalities
  • Resistant organisms
  • Renal or perinephric abscess

Prevention of Recurrent UTIs

• If recurrent infections are an issue, consider daily antibiotic prophylaxis 1
• Non-antimicrobial strategies:
  • Increased fluid intake
  • Vaginal estrogen in postmenopausal women
  • Methenamine hippurate as a non-antibiotic alternative 1

Key Pitfalls to Avoid

1. Treating asymptomatic bacteriuria - common in elderly but generally doesn't require treatment
2. Using fluoroquinolones empirically - high resistance rates limit their use 3
3. Inadequate duration of therapy - underdosing can lead to treatment failure
4. Failing to adjust for renal function - critical in elderly patients
5. Not obtaining cultures before starting antibiotics - essential for targeted therapy