Effectiveness of empiric aztreonam compared to other beta-lactams for treatment of Pseudomonas aeruginosa infections Michael Hogan,1 Mary Barna Bridgeman,1 Gee Hee Min,1 Deepali Dixit,1 Patrick J Bridgeman,1 Navaneeth Narayanan1,2 1Department of Pharmacy Practice and Administration, Ernest Mario School of Pharmacy, Rutgers University, Piscataway, NJ, USA; 2Division of Infectious Diseases, Department of Medicine, Rutgers Robert Wood Johnson Medical School, New Brunswick, NJ, USA 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%;