What antibiotic should be prescribed for a 113-pound patient with an uncomplicated urinary tract infection (UTI)?

Antibiotic Treatment for Uncomplicated UTI in a 113-pound Patient

For a 113-pound (51.3 kg) patient with uncomplicated UTI, nitrofurantoin 100 mg twice daily for 5 days is the recommended first-line treatment. 1

First-Line Treatment Options

The 2024 European Association of Urology (EAU) guidelines recommend the following first-line treatments for uncomplicated cystitis in women:

1. Nitrofurantoin:

   • Macrocrystals: 50-100 mg four times daily for 5 days
   • Monohydrate/macrocrystals: 100 mg twice daily for 5 days
   • Prolonged release: 100 mg twice daily for 5 days

2. Fosfomycin trometamol: 3 g single dose (one day)

3. Pivmecillinam: 400 mg three times daily for 3-5 days

Dosing Considerations for a 113-pound Patient

For a patient weighing 113 pounds (51.3 kg), standard adult dosing is appropriate as the patient's weight falls within the normal adult range. The recommended dosing does not require adjustment for this weight.

Treatment Algorithm

1. First choice: Nitrofurantoin 100 mg twice daily for 5 days

   • Excellent efficacy against most uropathogens
   • Low resistance rates
   • Minimal "collateral damage" (ecological effects on normal flora)
   • Achieves high concentrations in urine

2. Alternative if nitrofurantoin contraindicated:

   • Fosfomycin trometamol 3 g single dose
   • Trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days (if local resistance <20%)
   • Cephalosporins (e.g., cefadroxil 500 mg twice daily for 3 days) if local E. coli resistance <20%

Important Clinical Considerations

• Urine culture: Obtain a urine culture before initiating treatment to confirm the diagnosis and guide therapy if the initial treatment fails 1

• Treatment duration: Keep antibiotic treatment as short as reasonable, generally no longer than 7 days 1

• Avoid fluoroquinolones: Reserve for more complicated infections due to their ecological impact and potential for adverse effects 1

• Avoid unnecessary treatment: Do not treat asymptomatic bacteriuria 1

Common Pitfalls to Avoid

1. Overtreatment: Using broad-spectrum antibiotics for uncomplicated UTIs increases resistance risk

2. Inadequate follow-up: For patients whose symptoms do not resolve by the end of treatment or recur within 2 weeks, perform a urine culture and antimicrobial susceptibility testing 1

3. Inappropriate dosing: For nitrofurantoin, the twice-daily regimen (100 mg) is as effective as the four-times-daily regimen and improves compliance

4. Ignoring local resistance patterns: Treatment should be guided by local antibiograms when available

5. Treating without symptoms: Avoid treating asymptomatic bacteriuria as this contributes to antibiotic resistance without clinical benefit 1

For this 113-pound patient with uncomplicated UTI, nitrofurantoin 100 mg twice daily for 5 days provides the optimal balance of efficacy, safety, and antimicrobial stewardship.