What is the recommended treatment for a patient with a urinary tract infection caused by Klebsiella pneumoniae and Proteus mirabilis?

Treatment of Urinary Tract Infection Caused by Klebsiella pneumoniae and Proteus mirabilis

Based on the susceptibility testing results, amoxicillin-clavulanate is the most appropriate first-line treatment for this urinary tract infection caused by Klebsiella pneumoniae and Proteus mirabilis.

Analysis of Susceptibility Testing Results

The urine culture shows two organisms:

1. Klebsiella pneumoniae (>100,000 CFU/mL)
2. Proteus mirabilis (>100,000 CFU/mL)

Antibiotic Susceptibility Patterns:

Both organisms are susceptible to:

• Amoxicillin/clavulanate (S)
• Cefazolin (S)
• Ceftazidime (S)
• Ceftazidime/avibactam (S)
• Ceftriaxone (S)
• Cefuroxime (S)
• Gentamicin (S)
• Meropenem (S)
• Meropenem/vaborbactam (S)
• Piperacillin/tazobactam (S)
• Tobramycin (S)

Resistance patterns:

• Both organisms are resistant to ampicillin (R)
• P. mirabilis is resistant to ciprofloxacin (R), levofloxacin (R), nitrofurantoin (R), tetracycline (R), and trimethoprim/sulfamethoxazole (R)
• K. pneumoniae is intermediate to tetracycline (I) but susceptible to nitrofurantoin (S) and trimethoprim/sulfamethoxazole (S)

Treatment Recommendation Algorithm

1. First-line therapy: Amoxicillin-clavulanate

   • Dosage: Standard dosing of 875/125 mg orally twice daily for 7 days
   • Rationale: Both organisms are susceptible, it's an oral option, and it's effective for complicated UTIs 1

2. Alternative options (if amoxicillin-clavulanate cannot be used):

   • Cephalexin (based on cefazolin susceptibility)
   • Cefuroxime
   • Trimethoprim-sulfamethoxazole (only for K. pneumoniae; P. mirabilis is resistant)

3. For severe infection or treatment failure:

   • Parenteral options: Ceftriaxone, gentamicin, or meropenem

Rationale for Recommendation

Amoxicillin-clavulanate is recommended as the first-line treatment because:

1. Both organisms show susceptibility to this agent
2. It's an oral medication, allowing for outpatient treatment
3. It has good urinary penetration
4. It avoids the use of fluoroquinolones (ciprofloxacin/levofloxacin), to which P. mirabilis is resistant
5. It avoids nitrofurantoin, which is ineffective against P. mirabilis
6. It preserves broader-spectrum agents like carbapenems for more severe infections

Special Considerations

• Duration of therapy: 7 days is recommended for complicated UTIs with multiple organisms 1
• Follow-up: Clinical response should be assessed within 48-72 hours of starting treatment
• Persistent symptoms: If symptoms persist beyond 72 hours, consider:
  • Repeat urine culture
  • Changing antibiotics based on susceptibility
  • Evaluating for complications or anatomical abnormalities 1

Common Pitfalls to Avoid

1. Using nitrofurantoin: Despite K. pneumoniae being susceptible, P. mirabilis is resistant, making this an inappropriate choice
2. Using fluoroquinolones: P. mirabilis is resistant to ciprofloxacin and levofloxacin
3. Using trimethoprim-sulfamethoxazole: P. mirabilis is resistant, making this inappropriate as monotherapy
4. Using tetracyclines: Both organisms show resistance or intermediate susceptibility
5. Overuse of carbapenems: While both organisms are susceptible to meropenem, these should be reserved for more severe infections or treatment failures to prevent development of resistance 2

By selecting amoxicillin-clavulanate, you're choosing an effective agent that targets both organisms while practicing good antimicrobial stewardship.