What is the best antibiotic for an 88-year-old female with a urinary tract infection (UTI), chronic kidney disease (CKD) and impaired renal function, with urine culture results showing Escherichia coli and Enterococcus faecalis?

Best Antibiotic Treatment for UTI in 88-Year-Old Female with CKD

Ampicillin is the optimal antibiotic choice for this patient with UTI caused by both E. coli and E. faecalis, given her CKD with eGFR 32 and the susceptibility patterns shown in the culture results. 1

Analysis of Culture Results and Patient Factors

Organisms Identified:

• Escherichia coli (1x10^7 - 1x10^8 CFU/L)
• Enterococcus faecalis (1x10^7 - 1x10^8 CFU/L)

Susceptibility Patterns:

• E. coli: Susceptible to ampicillin, cephalexin, nitrofurantoin, gentamicin, and trimethoprim-sulfamethoxazole; Resistant to ciprofloxacin
• E. faecalis: Susceptible to ampicillin, ciprofloxacin, and nitrofurantoin; Resistant to tetracycline
• Note: Enterococcus species are uniformly resistant to all cephalosporins, clindamycin, and trimethoprim-sulfamethoxazole

Patient Factors:

• 88-year-old female
• CKD with eGFR 32, creatinine 124
• This classifies as a complicated UTI due to age and renal impairment 1

Treatment Decision Algorithm

1. Identify antibiotics effective against both organisms:

   • Ampicillin (susceptible for both)
   • Nitrofurantoin (susceptible for both but limited to uncomplicated lower UTI only)

2. Evaluate renal function considerations:

   • With eGFR 32, this patient has moderate renal impairment
   • Nitrofurantoin is contraindicated in patients with CrCl <30 ml/min due to ineffective urinary concentrations and increased toxicity risk
   • Ampicillin requires dose adjustment but can be safely used

3. Consider antibiotic coverage spectrum:

   • Ampicillin provides appropriate coverage for both identified organisms
   • No need for broader coverage as susceptibility is confirmed

Recommended Treatment

Ampicillin is the optimal choice because:

• It's effective against both isolated pathogens
• Can be safely used with appropriate dose adjustment in renal impairment
• Avoids unnecessary broad-spectrum coverage
• Follows the principle of using the narrowest effective antibiotic

Dosing Considerations:

• Standard ampicillin dosing should be adjusted for renal impairment
• For eGFR 30-50 ml/min: Consider 500 mg every 6-8 hours
• Duration: 7-14 days (longer duration due to complicated UTI status) 1

Alternative Options (if ampicillin cannot be used)

1. Gentamicin:

   • Effective against E. coli but requires careful dosing in renal impairment
   • For CKD with eGFR 32, dose should be approximately 35% of normal dose 2
   • Monitor drug levels and renal function closely
   • Not ideal as first choice due to nephrotoxicity risk in a patient with existing CKD

2. Ciprofloxacin:

   • Effective against E. faecalis but not E. coli (resistant)
   • Not recommended as empiric therapy for complicated UTI when resistance is present 1

Important Considerations

• Avoid nitrofurantoin despite susceptibility, as it's contraindicated in patients with CrCl <30 ml/min and the label specifically states "for uncomplicated lower UTI only" 3

• Avoid cephalosporins (including cephalexin) despite E. coli susceptibility, as Enterococcus species are intrinsically resistant to all cephalosporins 1

• Avoid trimethoprim-sulfamethoxazole despite E. coli susceptibility, as Enterococcus species are intrinsically resistant 1

• Monitor renal function throughout treatment as both the infection and antibiotics can affect kidney function

• Reassess therapy if clinical improvement is not seen within 48-72 hours

By choosing ampicillin, you're providing effective coverage against both pathogens while minimizing the risk of further renal impairment in this elderly patient with CKD.