What is the first-line antibiotic for a 16-year-old girl with a suspected urinary tract infection (UTI) and a history of previous UTIs?

First-Line Antibiotic for a 16-Year-Old Girl with Suspected UTI

For a 16-year-old girl with suspected UTI and history of previous UTIs, nitrofurantoin should be used as the first-line antibiotic treatment. 1

Recommended Treatment Algorithm

1. First-line options (in order of preference):

   • Nitrofurantoin (100 mg twice daily for 5 days)
   • Trimethoprim-sulfamethoxazole (160/800 mg twice daily for 3 days) - if local resistance patterns are <20%
   • Fosfomycin trometamol (3 g single dose)

2. Before initiating treatment:

   • Obtain urinalysis and urine culture with sensitivity testing
   • Treatment can be started while awaiting culture results

3. Duration of therapy:

   • As short as reasonable, generally 5 days for nitrofurantoin
   • No longer than 7 days for uncomplicated UTI

Rationale for Nitrofurantoin as First Choice

Nitrofurantoin is recommended as first-line therapy based on:

• High efficacy against common uropathogens: Maintains approximately 95.6% susceptibility against E. coli, the most common UTI pathogen 2
• Low resistance rates: Only 2.3% resistance compared to 24% for fluoroquinolones and 29% for trimethoprim-sulfamethoxazole 2
• Strong guideline support: Both the AUA and EAU guidelines list nitrofurantoin as a first-line agent 1
• Antibiotic stewardship: Helps preserve fluoroquinolones for more serious infections 3

Important Clinical Considerations

• Obtain cultures: For recurrent UTIs, obtain urinalysis and urine culture with each symptomatic episode before starting antibiotics 1
• Local resistance patterns: Consider local antibiograms when selecting therapy, particularly for trimethoprim-sulfamethoxazole 1
• Avoid nitrofurantoin in certain situations:
  • Suspected pyelonephritis (does not achieve adequate tissue concentrations)
  • Renal impairment
  • Last trimester of pregnancy

Common Pitfalls to Avoid

• Treating asymptomatic bacteriuria: Do not treat positive cultures without symptoms 1
• Prolonged therapy: Avoid treatment courses longer than 7 days for uncomplicated UTIs 1
• Fluoroquinolone overuse: Reserve these agents for more invasive infections due to increasing resistance and adverse effects 2, 4
• Failure to follow up: For symptoms that don't resolve or recur within 2 weeks, obtain repeat cultures and consider alternative antibiotics 1

For Recurrent UTIs

Since this patient has a history of UTIs, consider discussing preventive strategies after treating the acute episode:

• Patient-initiated treatment for future episodes
• Increased fluid intake
• Consideration of prophylactic options if she meets criteria for recurrent UTIs (≥3 UTIs/year or ≥2 in 6 months) 1, 5

The most recent guidelines consistently recommend nitrofurantoin as a first-line agent with excellent efficacy and favorable resistance patterns compared to alternatives, making it the optimal choice for this adolescent patient with a history of UTIs.