What antibiotic to prescribe for a 51-year-old female with cystitis who did not respond to Macrobid (nitrofurantoin)?

Antibiotic Selection After Nitrofurantoin Failure for Cystitis in a 51-Year-Old Female

Fosfomycin trometamol (3g single dose) is the most appropriate next-line therapy for a 51-year-old female with cystitis who failed nitrofurantoin treatment. 1

Rationale for Antibiotic Selection

When nitrofurantoin fails in the treatment of uncomplicated cystitis, it's important to select an alternative antibiotic with:

1. Different mechanism of action
2. Low resistance rates
3. Minimal collateral damage (ecological adverse effects)

First-Line Options After Nitrofurantoin Failure:

1. Fosfomycin trometamol (3g single dose) 1

   • Advantages:
     • Minimal resistance reported globally
     • Single-dose administration improves compliance
     • Minimal collateral damage to gut flora
     • Maintains efficacy against multidrug-resistant E. coli

2. Trimethoprim-sulfamethoxazole (160/800mg twice daily for 3 days) 1

   • Consider only if:
     • Local resistance rates are <20%
     • Patient hasn't used this medication in the past 3-6 months
     • Patient hasn't traveled outside the US in past 3-6 months
   • Caution: Increasing resistance rates limit empiric use

Second-Line Options (if first-line options cannot be used):

1. Fluoroquinolones (e.g., levofloxacin 750mg once daily for 5 days) 1, 2

   • Should be reserved due to:
     • Risk of serious adverse effects
     • Concerns about resistance
     • Collateral damage (selection of resistant organisms)
   • Consider when other options aren't feasible

2. β-lactams (3-7 day regimens) 1

   • Options include:
     • Amoxicillin-clavulanate
     • Cefdinir
     • Cefaclor
     • Cefpodoxime-proxetil
   • Note: Generally have inferior efficacy and more adverse effects compared to other UTI antibiotics

Clinical Approach After Nitrofurantoin Failure

1. Obtain urine culture and susceptibility testing 1, 3

   • Essential after treatment failure
   • Guides targeted therapy based on the specific pathogen

2. Consider patient-specific factors:

   • Recent antibiotic exposure (past 3-6 months)
   • Recent travel history (especially international)
   • Medication allergies or intolerances
   • Renal function (avoid nitrofurantoin if CrCl <60 mL/min) 3

3. Evaluate for complications or alternative diagnoses:

   • Symptoms suggesting pyelonephritis (fever, flank pain)
   • Structural abnormalities
   • Urinary retention
   • Immunocompromised status

Important Considerations

• Resistance patterns: Local resistance patterns should guide empiric therapy choices 1
• Collateral damage: Fluoroquinolones and broad-spectrum cephalosporins have greater ecological impact and should be reserved for situations where narrower-spectrum agents cannot be used 1
• Duration of therapy: Short-course therapy is as effective as longer treatment for uncomplicated UTIs with fewer adverse events 3
• Monitoring: Ensure clinical improvement within 48-72 hours; persistent symptoms warrant reassessment 3

Pitfalls to Avoid

• Avoid amoxicillin or ampicillin for empiric treatment due to poor efficacy and high resistance rates 1
• Don't repeat nitrofurantoin after failure, as this suggests resistance or another issue
• Don't assume treatment failure is always due to resistance - consider non-adherence, reinfection, or complicated UTI
• Avoid fluoroquinolones as routine second-line therapy due to FDA warnings about serious adverse effects and the need to preserve effectiveness 1, 2

Remember that nitrofurantoin failure may indicate the presence of a resistant organism or a complicated UTI requiring more comprehensive evaluation and management.