First-Line Antibiotics for Uncomplicated UTI in a 15-Year-Old
For a healthy 15-year-old with uncomplicated UTI and acceptable local E. coli resistance, prescribe nitrofurantoin 100 mg twice daily for 5 days, trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days (if local resistance <20%), or fosfomycin 3 g single dose. 1
Recommended First-Line Agents
The 2024 WHO guidelines explicitly recommend three first-choice antibiotics for lower urinary tract infections: nitrofurantoin, trimethoprim-sulfamethoxazole, and amoxicillin-clavulanate 1. These agents were selected based on equivalent efficacy to fluoroquinolones while minimizing collateral damage (selection of multidrug-resistant organisms) 1.
Nitrofurantoin
- Dosing: 100 mg twice daily for 5 days 1, 2
- Demonstrates equivalent efficacy to trimethoprim-sulfamethoxazole for short-term and long-term symptomatic cure (RR 0.99,95% CI 0.95-1.04 and RR 1.01,95% CI 0.94-1.09, respectively) 1
- Maintains high susceptibility rates globally with minimal resistance development 1
- Avoid if: upper tract involvement (pyelonephritis) is suspected, as nitrofurantoin has insufficient tissue penetration 3, 4
Trimethoprim-Sulfamethoxazole (TMP-SMX)
- Dosing: 160/800 mg twice daily for 3 days 1
- Critical caveat: Only use if local E. coli resistance rates are <20% 1, 5
- Shows equivalent efficacy to fluoroquinolones for uncomplicated cystitis (RR 1.00,95% CI 0.97-1.03 for short-term cure) 1
- Avoid if: patient received TMP-SMX in the preceding 3-6 months, as prior use is an independent risk factor for resistance 1
Fosfomycin
- Dosing: 3 g single oral dose 1, 2
- Excellent option with minimal resistance and good safety profile 1
- Single-dose regimen shows similar clinical and bacteriological efficacy to 3-7 day courses of alternative agents 2
- Recent data in female adolescents (median age 13 years) demonstrated 97% clinical cure and 94% microbiological cure rates for MDR E. coli 6
- FDA-approved only for uncomplicated cystitis in women; not indicated for pyelonephritis 3
Second-Line Options
Amoxicillin-Clavulanate
- Dosing: Standard dosing for 3-7 days 1
- Listed as first-choice by WHO but considered second-line by IDSA due to inferior efficacy compared to other agents 1
- Appropriate when first-line agents cannot be used 1
- Avoid if: patient received β-lactam within preceding 3 months or local resistance exceeds 20% 7
Oral Cephalosporins
- Options include cefdinir, cefaclor, cefpodoxime-proxetil for 3-7 days 1
- Generally have inferior efficacy and more adverse effects compared to first-line agents 1
- Should be used with caution and only when other recommended agents cannot be used 1
Agents to Avoid
Fluoroquinolones (Ciprofloxacin, Levofloxacin)
- Should be reserved for important uses other than acute cystitis despite high efficacy 1
- Propensity for collateral damage (selection of multidrug-resistant organisms) 1
- Fluoroquinolones were deliberately excluded from WHO recommendations because sufficient alternatives exist 1
- Only consider if local resistance <10% and patient has no recent fluoroquinolone exposure 1
Amoxicillin or Ampicillin Alone
- Should not be used for empirical treatment due to very high global resistance rates (median 75%, range 45-100% of E. coli isolates) 1
- Relatively poor efficacy even when susceptible 1
Treatment Duration Considerations
- 3-day regimens are appropriate for TMP-SMX 1
- 5-day regimens are recommended for nitrofurantoin 1, 2
- Single-dose fosfomycin is sufficient 3, 2, 6
- Treat for no longer than 7 days for uncomplicated cystitis 1
Critical Pitfalls to Avoid
- Do not use moxifloxacin for UTI treatment due to uncertain urinary concentrations 1, 7
- Do not treat asymptomatic bacteriuria unless patient is pregnant or undergoing urological procedures 1
- Obtain urine culture before treatment if patient has recurrent UTIs or recent antibiotic exposure 1, 7
- Avoid empiric fluoroquinolones when local resistance exceeds 10% or patient has recent fluoroquinolone exposure 1