Aztreonam for Urinary Tract Infections
Aztreonam (Azactam) is effective for treating urinary tract infections caused by susceptible gram-negative bacteria, particularly in complicated UTIs where other antibiotics may not be suitable due to resistance patterns or allergies.
FDA-Approved Indications
Aztreonam is FDA-approved for both complicated and uncomplicated urinary tract infections, including pyelonephritis and cystitis (initial and recurrent) caused by:
- Escherichia coli
- Klebsiella pneumoniae
- Proteus mirabilis
- Pseudomonas aeruginosa
- Enterobacter cloacae
- Klebsiella oxytoca
- Citrobacter species
- Serratia marcescens 1
Efficacy in UTIs
Clinical studies have demonstrated good efficacy of aztreonam in treating complicated UTIs:
- Overall clinical efficacy rate of 64% in complicated UTIs 2
- Bacteriologic cure rates of 96-98% for multidrug-resistant gram-negative bacteria in UTIs 3
- Particularly effective against Pseudomonas aeruginosa with 60% elimination rate 2
Positioning in Treatment Algorithm
First-line therapy:
- Aztreonam is not typically a first-line agent for uncomplicated UTIs
- For empiric treatment of uncomplicated cystitis, nitrofurantoin, fosfomycin, or pivmecillinam are preferred
Appropriate use scenarios:
- Beta-lactam allergies: Aztreonam can be used in patients with severe allergies to penicillins or cephalosporins as it has minimal cross-reactivity
- Resistant gram-negative infections: Useful for infections with multidrug-resistant gram-negative bacteria
- Targeted therapy: When culture results confirm susceptibility to aztreonam
Special Considerations for CRE Infections
For carbapenem-resistant Enterobacterales (CRE) UTIs:
- Aztreonam alone is not recommended for CRE infections
- It has unique activity against metallo-beta-lactamase (MBL)-producing CRE, but as monotherapy does not cover other broad-spectrum beta-lactamases or carbapenemases 4
- For MBL-producing CRE, combination therapy may be necessary
Dosing Recommendations
- Standard dosing: 1-2 grams IV every 8-12 hours
- For complicated UTIs: 2 grams IV twice daily has shown good efficacy 5
- Duration: 7-14 days (14 days for men when prostatitis cannot be excluded)
Advantages and Limitations
Advantages:
- Excellent gram-negative coverage
- Minimal cross-reactivity with beta-lactam allergies
- Good safety profile with minimal side effects 3
Limitations:
- No activity against gram-positive or anaerobic organisms
- Should not be used as monotherapy when these pathogens are suspected
- Concurrent therapy with other antimicrobials is recommended for seriously ill patients at risk of gram-positive infections 1
Monitoring and Safety
- Side effects are generally minimal and transient 3
- Most common adverse effects: diarrhea, abdominal discomfort, transaminase elevations, and eosinophilia 2
- These typically resolve after discontinuation of the drug
Important Cautions
- Certain antibiotics (e.g., cefoxitin, imipenem) may induce high levels of beta-lactamase in some gram-negative bacteria, potentially causing antagonism to aztreonam
- These beta-lactamase-inducing antibiotics should not be used concurrently with aztreonam 1
- Always obtain urine culture before starting treatment and adjust therapy based on susceptibility results
Aztreonam remains a valuable option in the antimicrobial armamentarium for UTIs, particularly for patients with beta-lactam allergies or infections caused by susceptible multidrug-resistant gram-negative pathogens.