What antibiotics are used to treat urinary tract infections (UTIs) caused by various bacteria?

Antibiotic Treatment for Various Bacteria in Urinary Tract Infections

For urinary tract infections (UTIs), first-line antibiotics should be nitrofurantoin, trimethoprim-sulfamethoxazole (TMP-SMX), or amoxicillin-clavulanic acid, with selection based on local resistance patterns and specific bacterial pathogens. 1

Treatment Algorithm Based on UTI Classification

Lower Uncomplicated UTIs

• First-choice options:

  • Nitrofurantoin 100mg twice daily for 5 days
  • Trimethoprim-sulfamethoxazole 160/800mg twice daily for 3 days
  • Amoxicillin-clavulanic acid (dosage per local guidelines)

• Second-choice option:

  • Fosfomycin 3g single dose (not recommended by WHO committee due to lower clinical and microbiological resolution compared to nitrofurantoin) 1

Upper UTIs (Pyelonephritis/Prostatitis)

• Mild to Moderate:

  • First choice: Ciprofloxacin (if local E. coli resistance <10%)
  • Second choice: Ceftriaxone or cefotaxime

• Severe:

  • First choice: Ceftriaxone or cefotaxime
  • Second choice: Amikacin (preferred over gentamicin due to better resistance profile) 1

Antibiotic Selection Based on Common Bacterial Pathogens

Escherichia coli (most common - 55.2% of UTIs)

• First-line: Nitrofurantoin (96.7-98.9% susceptibility) or TMP-SMX (if local resistance <20%) 2
• For resistant strains: Fosfomycin (95.3-100% susceptibility) 2
• For ESBL-producing E. coli: Nitrofurantoin, fosfomycin, or carbapenems 3

Enterococcus faecalis (18% of UTIs)

• First-line: Nitrofurantoin or amoxicillin-clavulanic acid
• Alternative: Fosfomycin (high activity) 2, 4

Klebsiella species (10.3% of UTIs)

• First-line: Amoxicillin-clavulanic acid (Klebsiella is intrinsically resistant to amoxicillin alone)
• For ESBL-producing Klebsiella: Carbapenems or aminoglycosides 3
• Note: Lower fosfomycin susceptibility (36-38%) compared to E. coli 4

Pseudomonas aeruginosa

• Options: Ciprofloxacin, ceftazidime, piperacillin-tazobactam
• For MDR strains: Consider ceftolozane-tazobactam, ceftazidime-avibactam 3

Proteus mirabilis

• First-line: TMP-SMX or ciprofloxacin
• Alternative: Amoxicillin-clavulanic acid 1

Duration of Treatment

• Lower UTI: Short course (3-5 days) 1
• Upper UTI/complicated: 7-14 days 5
• Single-dose antibiotics (except fosfomycin) are associated with higher rates of bacteriological persistence and should be avoided 1

Important Clinical Considerations

Culture and Susceptibility Testing

• Obtain urine culture before starting antibiotics for:
  • Suspected pyelonephritis
  • Complicated UTIs
  • Recurrent UTIs
  • Treatment failure
  • Recent antibiotic exposure 1

Resistance Considerations

• E. coli resistance to amoxicillin: Median 75% globally (avoid as monotherapy) 1
• Fluoroquinolones (ciprofloxacin/levofloxacin):
  • Reserve as second-line due to:
    • FDA warnings about serious side effects (tendon, muscle, joint, nerve damage)
    • Increasing resistance rates
    • Collateral damage to gut microbiome 1, 5
  • Only use if local resistance <10% and benefits outweigh risks 1, 5

Special Populations

• Pregnant women: Avoid TMP-SMX and fluoroquinolones
• Elderly patients: Avoid nitrofurantoin if CrCl <60 mL/min 5
• Males: UTIs generally considered complicated; longer treatment duration required 5

Asymptomatic Bacteriuria

• Do not treat asymptomatic bacteriuria except in pregnancy or before urologic procedures 1
• Avoid surveillance urine cultures in asymptomatic patients with history of recurrent UTIs 1

Emerging Resistance Management

• For carbapenem-resistant Enterobacteriaceae (CRE), options include ceftazidime-avibactam, meropenem-vaborbactam, or imipenem-cilastatin-relebactam 3
• For multidrug-resistant organisms, consider consulting infectious disease specialists for optimal therapy selection

By following this evidence-based approach to antibiotic selection based on UTI classification and bacterial pathogen, clinicians can optimize treatment outcomes while practicing good antimicrobial stewardship.