Effectiveness of empiric aztreonam compared to other beta-lactams for treatment of Pseudomonas aeruginosa infections

Purpose: To evaluate the use of aztreonam as an active empiric therapy against subsequent culture of Pseudomonas aeruginosa (P. aeruginosa). Methods: This was a retrospective cohort study conducted among patients who received either aztreonam or an antipseudomonal beta-lactam (BL,) as an empiric therapy with subsequent culture with P. aeruginosa. All patients with at least one positive culture for P. aeruginosa between January 2014 and August 2016 were included in this analysis. The primary composite outcome was empiric therapy failure, defined as inappropriate empiric therapy, alteration of empiric antibiotic following culture results, or 30-day in-hospital mortality. Secondary outcomes included appropriate empiric therapy, alteration of empiric therapy, 30-day-in-hospital mortality, and post-culture hospital length of stay. Results: The primary outcome of empiric therapy failure was significantly higher in the aztreonam group than in the BL group (77.8% vs 41.9%; P=0.004). The aztreonam group had a lower rate of appropriate empiric therapy compared with the BL group (44.4% vs 66.1%; P=0.074) and higher alteration of empiric therapy once susceptibilities were known than when compared with the 1W group (61.1%vs 28.2%; P=0.005). Although numerically higher, 30-day-in-hospital mortality and median hospital length of stay were not significantly different between the two groups. Conclusion: Empiric therapy failure occurred more often when initially using aztreonam vs a BL, in a patient who subsequently had a P. aeruginosa infection. Only a third of patients within the aztreonam group had a documented BL allergy, demonstrating an inclination for clinicians to utilize this drug as an empiric therapy when there were more appropriate therapies available.