What are the recommended antibiotic treatments and dosages for uncomplicated and complicated urinary tract infections?

Antibiotic Treatment for Urinary Tract Infections

First-Line Treatment for Uncomplicated UTIs

For uncomplicated UTIs in otherwise healthy non-pregnant women, first-line treatment options include nitrofurantoin 100mg twice daily for 5 days, fosfomycin 3g single dose, or trimethoprim-sulfamethoxazole 160/800mg twice daily for 3 days, with selection based on local resistance patterns. 1

These recommendations are supported by multiple guidelines, with specific considerations:

• Nitrofurantoin: 100mg orally twice daily for 5 days

  • Contraindicated in renal impairment (CrCl <60 mL/min) 1, 2
  • Excellent activity against E. coli and other common uropathogens 2
  • Avoid in last trimester of pregnancy 2

• Fosfomycin: 3g oral single dose

  • Convenient single-dose regimen with minimal drug interactions 1
  • Effective against VRE and many resistant organisms 1, 3
  • Not recommended for males due to limited efficacy evidence 1

• Trimethoprim-sulfamethoxazole: 160/800mg twice daily for 3 days

  • Only use if local E. coli resistance is <20% 4
  • Monitor renal function due to renal elimination 1
  • Avoid in pregnancy 1

Alternative Treatments for Uncomplicated UTIs

Fluoroquinolones (e.g., ciprofloxacin 250mg twice daily for 3 days) should be reserved as alternative agents due to:

• Risk of serious adverse effects
• Increasing resistance rates
• FDA warnings about safety concerns 4, 1
• Should only be used if local E. coli resistance is <10% 1

β-Lactams (including amoxicillin-clavulanate, cefdinir, cefaclor, and cefpodoxime-proxetil) are appropriate when other recommended agents cannot be used, but generally have inferior efficacy and more adverse effects 4.

Treatment for Complicated UTIs

For complicated UTIs (including those in males, pregnant women, patients with structural/functional abnormalities, or immunocompromised patients):

Parenteral Options:

• Ceftazidime/avibactam: 2.5g IV q8h (5-7 days) 4
• Meropenem/vaborbactam: 4g IV q8h (5-7 days) 4
• Imipenem/cilastatin/relebactam: 1.25g IV q6h (5-7 days) 4
• Aminoglycosides:
  • Gentamicin: 5-7 mg/kg/day IV once daily (5-7 days) 4
  • Amikacin: 15 mg/kg/day IV once daily (5-7 days) 4
  • Plazomicin: 15 mg/kg IV q12h (5-7 days) 4
• Cefepime: 1-2g IV every 12 hours (7-10 days) 5

For VRE UTIs:

• Complicated VRE UTIs:

  • Linezolid 600mg IV q12h (5-7 days)
  • Daptomycin 6-12 mg/kg IV once daily (5-7 days) 4

• Uncomplicated VRE UTIs:

  • Fosfomycin 3g PO single dose or every other day
  • Nitrofurantoin 100mg PO four times daily
  • Ampicillin 18-30g/day IV in divided doses
  • Amoxicillin 500mg PO/IV q8h (3-7 days) 4

Treatment Based on Specific Pathogens

For ESBL-producing Enterobacterales:

• Nitrofurantoin (for uncomplicated UTIs)
• Fosfomycin (for uncomplicated UTIs)
• Carbapenems (preferably ertapenem) 1, 6

For Carbapenem-resistant Enterobacterales (CRE):

• Ceftazidime-avibactam
• Meropenem-vaborbactam
• Imipenem-cilastatin-relebactam 1, 6

Pediatric Dosing

For pediatric patients up to 40kg:

• 50 mg/kg/dose every 12 hours for uncomplicated and complicated UTIs
• Treatment duration similar to adults 5

Treatment Duration

• Uncomplicated cystitis:

  • Fosfomycin: single dose
  • Nitrofurantoin: 5 days
  • TMP-SMX: 3 days 1

• Complicated UTIs or pyelonephritis: 7-14 days 1

Considerations for Special Populations

Elderly Patients:

• Nitrofurantoin if renal function is adequate
• Avoid fluoroquinolones due to increased risk of adverse effects 1

Pregnant Women:

• Avoid TMP-SMX and fluoroquinolones
• Nitrofurantoin or cephalosporins are recommended (avoid nitrofurantoin in last trimester) 1, 2

Renal Impairment:

Dose adjustments required for most antibiotics. For cefepime:

• CrCl 30-60 mL/min: 2g every 24 hours
• CrCl 11-29 mL/min: 1g every 24 hours
• CrCl <11 mL/min: 500mg every 24 hours 5

Clinical Pearls

1. Always obtain urine culture before starting therapy for complicated UTIs and adjust treatment based on susceptibility results 1

2. Expect clinical improvement within 48-72 hours; if not seen, reevaluate diagnosis and treatment 1

3. Amoxicillin or ampicillin should not be used for empirical treatment due to poor efficacy and high resistance rates 4

4. For recurrent UTIs, consider non-antimicrobial preventive strategies such as increased fluid intake, vaginal estrogen in postmenopausal women, or methenamine hippurate 1

5. Fosfomycin susceptibility testing is complicated; agar dilution is the reference method but Etest is a viable alternative with 94% agreement 3