What is the recommended antibiotic for an uncomplicated urinary tract infection (UTI)?

First-Line Antibiotics for Uncomplicated Urinary Tract Infection

Nitrofurantoin (100 mg twice daily for 5 days) is the recommended first-line antibiotic for uncomplicated urinary tract infections due to its minimal resistance patterns, limited collateral damage to gut flora, and excellent efficacy. 1

First-Line Treatment Options

The most recent guidelines recommend the following first-line options for uncomplicated UTIs:

1. Nitrofurantoin (100 mg twice daily for 5 days)

   • Excellent efficacy with minimal resistance patterns
   • Limited collateral damage to gut flora
   • Recommended by both European Association of Urology and American Urological Association 1

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

   • Should only be used if local resistance is <20% 1, 2
   • Traditional first-line agent but rising resistance rates have affected its recommendation status 2
   • FDA-approved for UTIs caused by susceptible strains of E. coli, Klebsiella, Enterobacter, Morganella morganii, and Proteus species 3

3. Fosfomycin (single 3g dose)

   • Slightly lower efficacy than nitrofurantoin 1
   • Convenient single-dose regimen
   • More expensive than nitrofurantoin 2

Treatment Algorithm Based on Patient Factors

1. For most patients with uncomplicated UTI:

   • Start with nitrofurantoin 100 mg twice daily for 5 days 1, 4

2. If local resistance patterns show <20% resistance to trimethoprim-sulfamethoxazole:

   • Consider trimethoprim-sulfamethoxazole 160/800 mg twice daily for 3 days 2, 3

3. If patient needs single-dose convenience:

   • Consider fosfomycin 3g single dose 1

4. If patient has renal impairment:

   • Avoid nitrofurantoin if CrCl <30 mL/min 5
   • Adjust trimethoprim-sulfamethoxazole dosing based on creatinine clearance 3:
     • CrCl >30 mL/min: Standard regimen
     • CrCl 15-30 mL/min: Half the usual regimen
     • CrCl <15 mL/min: Not recommended

Important Considerations and Pitfalls

• Avoid fluoroquinolones for uncomplicated UTIs despite their high efficacy. They should be reserved for more serious infections due to their propensity for collateral damage and safety issues affecting tendons, muscles, joints, nerves, and the central nervous system 2

• Avoid amoxicillin or ampicillin for empirical treatment due to poor efficacy and high prevalence of antimicrobial resistance worldwide 2

• β-Lactam agents (including amoxicillin-clavulanate, cefdinir, cefaclor, and cefpodoxime-proxetil) should only be used when other recommended agents cannot be used, as they generally have inferior efficacy and more adverse effects 2

• Beware of misdiagnosing asymptomatic bacteriuria as UTI, which can lead to unnecessary antibiotic therapy 4

• Do not obtain routine post-treatment urinalysis or cultures for asymptomatic patients 1

• For pregnant patients, fosfomycin, cefalexin, or amoxicillin-clavulanate are appropriate options 1

The resurgence of nitrofurantoin in treatment guidelines is due to its maintained efficacy against common uropathogens despite decades of use, with E. coli maintaining high susceptibility rates 5, 6. While nitrofurantoin has historically been associated with adverse effects in long-term use, recent studies have shown good efficacy and tolerability in short-term therapy 6.

Duration of Treatment

• Uncomplicated UTIs: 3-5 days 1
• Complicated UTIs: 7-10 days 1
• Pyelonephritis: 10-14 days 1

Following these evidence-based recommendations will help ensure effective treatment while minimizing the risk of antibiotic resistance.