239 - Outcomes Associated with Empiric Aztreonam Use Compared to Anti-Pseudomonal β-lactams in Patients with Sepsis: An Opportunity for Allergy Stewardship

Background: Aztreonam is often given to patients with a documented β-lactam allergy in lieu of a first-line anti-pseudomonal β-lactam (APBL).  However, aztreonam offers no gram positive coverage and data suggest that gram negative organisms have lower susceptibility rates to this antibiotic than to APBLs.  Septic patients are especially vulnerable to poor outcomes since inappropriate initial antimicrobial therapy has been shown to be an independent predictor of increased mortality. The purpose of this study was to determine whether septic patients treated with aztreonam experience inferior outcomes compared to those treated with an APBL.

Methods: This was a retrospective, multicenter, cohort study of all adult patients in metro Charlotte Atrium Health facilities treated for sepsis or septic shock from January 2014 to October 2017.  Patients receiving either aztreonam or an APBL were identified using the system-wide sepsis database and enrolled in a 1:2 ratio.  Patients were excluded if there was no infection-related discharge ICD-9 or ICD-10 code, if they received both aztreonam and an APBL in the first 8 hours, or if they received fewer than 2 doses of the study antibiotic.  The primary endpoint was in-hospital mortality.

Results: A total of 194 patients received aztreonam and 388 patients received an APBL.  β-lactam allergies were more common in patients who received aztreonam compared to APBL (97% vs. 14.2%, p < 0.01). In-hospital mortality rates were greater in the patients who received aztreonam vs. APBL (22.7% vs. 12.9%, p = 0.0025).  After adjusting for APACHE II score, initial aztreonam exposure remained independently associated with hospital mortality (OR = 1.74, 95% CI: 1.0 – 2.8, p = 0.02).  Additionally, we identified an increase in combination therapy with the use of aminoglycosides (28.9% vs. 12.4%, p < 0.0001) and fluoroquinolones (50.5% vs. 25.8%, p < 0.0001) in patients receiving aztreonam.  No difference was found in overall length of stay or ICU length of stay.

Conclusion: In septic patients, the use of aztreonam as the backbone of antimicrobial therapy may result in increased mortality.  This highlights the importance of stewardship interventions that obtain an accurate allergy history and encourage the use of APBL antibiotics whenever feasible.