What medication is contraindicated in an 81-year-old woman with Impaired renal function (creatinine clearance < 25 mL/min), presenting with symptoms of a urinary tract infection (UTI)?

Nitrofurantoin is Contraindicated in Patients with Severe Renal Impairment

Nitrofurantoin is contraindicated in this 81-year-old woman with a creatinine clearance of <25 mL/min presenting with UTI symptoms. This is the correct answer (option A) because nitrofurantoin requires adequate renal function to achieve therapeutic concentrations in the urine and is contraindicated in patients with severe renal impairment 1.

Rationale for Contraindication of Nitrofurantoin

• The European Urology guidelines specifically recommend against using nitrofurantoin in patients with creatinine clearance <30 mL/min 1
• With severe renal impairment (CrCl <25 mL/min):
  • Nitrofurantoin fails to achieve adequate urinary concentrations for antimicrobial efficacy
  • Risk of toxicity increases due to drug accumulation
  • Peripheral neuropathy and pulmonary reactions are more likely to occur

Alternative Antibiotic Options for This Patient

Given the patient's severe renal impairment, the following alternatives would be more appropriate:

1. Amoxicillin (Option C):

   • Can be used in renal impairment with appropriate dose adjustment 2
   • Dosage should be modified based on the degree of renal impairment

2. Ceftriaxone (Option D):

   • No significant dose adjustment needed in renal impairment
   • Appropriate for more severe UTIs or when parenteral therapy is needed

3. Metronidazole (Option B):

   • While primarily used for anaerobic infections, it can be used in renal impairment
   • May require monitoring in elderly patients with decreased liver function 3

Antibiotic Selection Algorithm for UTI in Elderly with Renal Impairment

1. Assess severity of infection:

   • Uncomplicated vs. complicated UTI
   • Presence of systemic symptoms (fever, altered mental status)

2. Consider local resistance patterns:

   • If E. coli resistance to trimethoprim/sulfamethoxazole exceeds 20%, consider alternatives 1

3. Select appropriate antibiotic based on renal function:

   • CrCl <30 mL/min: Avoid nitrofurantoin
   • Consider amoxicillin with dose adjustment, cephalosporins, or fluoroquinolones with appropriate renal dosing

4. Adjust duration of therapy:

   • 7 days for uncomplicated UTI in elderly patients
   • 7-10 days for complicated UTI 1

Important Clinical Considerations

• Elderly patients often present with atypical UTI symptoms including confusion, altered mental status, and functional decline rather than classic dysuria and frequency 1
• Monitor renal function regularly during treatment, especially with potentially nephrotoxic antibiotics 1
• Ensure adequate hydration unless contraindicated to maintain urine output of approximately 1 L/24 hours 1
• Reassess in 48-72 hours to evaluate clinical response; if symptoms persist or worsen, obtain urine culture and consider alternative antibiotics 1

Common Pitfalls to Avoid

• Using nitrofurantoin in patients with CrCl <30 mL/min due to both reduced efficacy and increased toxicity risk
• Failing to adjust antibiotic dosages in patients with renal impairment
• Treating asymptomatic bacteriuria, which is common in older adults and does not require treatment 1
• Overlooking the need to discontinue or minimize other nephrotoxic drugs during UTI treatment 1

In conclusion, nitrofurantoin (option A) is the contraindicated medication in this elderly patient with severe renal impairment presenting with UTI symptoms.