Pseudomonas aeruginosa is a nosocomial pathogen capable of exhibiting a variety of resistance mechanisms against multiple classes of antibiotics. Fluoroquinolones, commonly used to treat a variety of infections in both ambulatory and hospitalized patients, have been increasingly linked to the development of resistance, both to fluoroquinolones and to other classes of antibiotics including β-lactams, cephalosporins, and carbapenems. In turn, as many as 95% of multidrug-resistant pseudomonal isolates may be resistant to fluoroquinolones. Although research has examined the effect of fluoroquinolone use on P. aeruginosa resistance, to our knowledge, no work has been published describing possible differences among individual fluoroquinolones related to resistance to other antibiotic classes. The purpose of this analysis was to assess the possible effects of varying usage of levofloxacin, gatifloxacin, and moxifloxacin on P. aeruginosa susceptibility to piperacillin-tazobactam, cefepime, and tobramycin. Data from January 2000 through December 2008 were obtained from clinical microbiology and pharmacy databases of the Medical University of South Carolina Medical Center, which is a 689-bed academic medical center and level 1 trauma center with adult and pediatric beds. This study was approved by the institution's institutional review board.