Is Polymyxin B (antibiotic) effective for treating urinary tract infections (UTIs)?

Polymyxin B for Urinary Tract Infections

Polymyxin B is effective for treating urinary tract infections caused by susceptible strains of multidrug-resistant gram-negative bacteria, particularly when less toxic antibiotics are ineffective or contraindicated. 1

Indications for Polymyxin B in UTIs

• Polymyxin B is FDA-approved for urinary tract infections caused by susceptible strains of Pseudomonas aeruginosa and Escherichia coli 1
• It should be reserved for treating infections produced by bacteria showing resistance to all beta-lactams, fluoroquinolones, and other first-line agents 2
• Polymyxin B is considered a drug of last resort for carbapenem-resistant gram-negative bacterial (CRGNB) infections, including those causing UTIs 2

First-Line Treatment Options for UTIs

• First-line antibiotics for uncomplicated UTIs include:
  • Amoxicillin-clavulanic acid 2
  • Nitrofurantoin 2
  • Sulfamethoxazole-trimethoprim 2
• For pyelonephritis and prostatitis:
  • Ciprofloxacin (if local resistance patterns allow) 2
  • Ceftriaxone or cefotaxime 2

Polymyxin B Dosing for UTIs

• Loading dose: 2-2.5 mg/kg 2
• Maintenance dose: 1.5-3 mg/kg/day divided in two doses 2
• No dosage adjustment is necessary for patients on continuous renal replacement therapy 2
• For patients with normal renal function, polymyxin B may be less nephrotoxic than colistin 2

Efficacy of Polymyxin B for UTIs

• Microbiological clearance rates of 88% have been reported in patients with MDR gram-negative bacteremia or UTIs treated with polymyxin B 3
• A more recent study showed 56.2% microbiological clearance of targeted bacteria after polymyxin B therapy 4
• Polymyxin B combination therapy is recommended over monotherapy for treating CRGNB infections in patients who require polymyxin treatment 2

Safety Considerations

Nephrotoxicity

• Nephrotoxicity occurs in approximately 24.7-45.8% of patients receiving polymyxin B 5, 4
• Risk factors for nephrotoxicity include:
  • Higher daily dose by actual body weight (HR = 1.73) 5
  • Concurrent use of vancomycin (HR = 1.89) 5
  • Concurrent use of contrast media (HR = 1.79) 5
  • Older age (76 vs. 59 years, p = 0.02) 6

Neurotoxicity

• Neurotoxicity can manifest as oral paresthesia and lower extremity paresthesias 7
• These symptoms are typically reversible upon discontinuation of polymyxin B 7
• Reversible numbness has been reported in some cases 4

Treatment Algorithm for UTIs When Considering Polymyxin B

1. First, attempt treatment with first-line agents (nitrofurantoin, TMP-SMX, fosfomycin) 2
2. If first-line treatment fails or susceptibility testing shows resistance:
   • Consider second-line agents based on susceptibility testing 2
3. Reserve polymyxin B for:
   • Infections caused by multidrug-resistant organisms 1
   • Cases where less toxic alternatives have failed or are contraindicated 1
   • UTIs caused by carbapenem-resistant gram-negative bacteria 2

Monitoring During Polymyxin B Therapy

• Monitor renal function regularly during treatment 2
• Consider therapeutic drug monitoring where available 2
• Avoid concurrent use of other nephrotoxic or ototoxic drugs 2
• Watch for signs of neurotoxicity, including paresthesias 7

Conclusion

While polymyxin B is effective for treating UTIs caused by multidrug-resistant gram-negative bacteria, it should be reserved for cases where first-line and second-line agents are ineffective due to its potential for nephrotoxicity and neurotoxicity. When used, appropriate dosing, monitoring, and consideration of risk factors for adverse effects are essential to maximize efficacy while minimizing harm.