Is Aztreonam effective against E. coli urinary tract infections (UTIs)?

Aztreonam is Effective Against E. coli UTIs

Aztreonam is highly effective for treating urinary tract infections caused by E. coli, with bacteriologic cure rates of 96-98% reported in clinical studies. 1, 2 As a monobactam antibiotic, aztreonam specifically targets gram-negative bacteria, including E. coli, which is one of the most common causative pathogens in UTIs.

Mechanism and Spectrum of Activity

Aztreonam has a unique spectrum of activity that makes it particularly suitable for UTIs caused by gram-negative bacteria:

• Selectively active against aerobic gram-negative bacteria, including E. coli
• FDA-approved specifically for urinary tract infections (both complicated and uncomplicated) caused by E. coli 1
• No activity against gram-positive bacteria or anaerobes, making it a targeted therapy 3
• Maintains effectiveness against many multidrug-resistant gram-negative pathogens 2

Dosing for UTIs

For urinary tract infections caused by E. coli, the recommended dosing is:

• 1-2 grams IV every 8-12 hours 4
• Duration typically 7-14 days, depending on infection severity
• Lower doses (0.5g twice daily) have shown 96% bacteriologic cure rates in complicated UTIs 2

Clinical Evidence

Clinical studies have demonstrated excellent outcomes when using aztreonam for E. coli UTIs:

• A study of 145 patients with complicated UTIs caused by multidrug-resistant bacteria (including 24 with E. coli) showed bacteriologic cure rates of 96-98% 2
• Aztreonam has been shown to be as effective or more effective than cefamandole in treating UTIs 3, 5
• Particularly valuable for infections caused by bacteria resistant to aminopenicillins and first/second-generation cephalosporins 2

Important Considerations

1. Antibiotic Stewardship: Aztreonam has become a target for antibiotic stewardship efforts due to its cost and specialized use 6. Reserve it for patients with true indications, such as:

   • Documented E. coli UTIs resistant to other antibiotics
   • Patients with severe penicillin allergies

2. Penicillin Allergy: Aztreonam is safe for patients with penicillin or cephalosporin allergies as there is no cross-reactivity for IgE- or T-cell-mediated hypersensitivity between penicillins and aztreonam 6

3. Combination Therapy: For empiric therapy when the causative organism is unknown, consider adding coverage for gram-positive bacteria, as aztreonam has no activity against these organisms 1, 7

Potential Limitations

• Minimal effect on indigenous fecal anaerobes when used alone 3
• Must be administered intravenously or intramuscularly for systemic infections due to very low oral bioavailability 3
• Not effective against gram-positive bacteria, so additional coverage may be needed if mixed infection is suspected 1

Aztreonam represents an excellent targeted therapy for E. coli UTIs, particularly in patients with beta-lactam allergies or infections caused by multidrug-resistant organisms. Its high efficacy rates and favorable safety profile make it a valuable option in the antimicrobial armamentarium for treating these infections.