Clinical and Microbiological Impact of Inhaled Tobramycin Treatment on Cystic Fibrosis Patients with Pseudomonas aeruginosaFrancesca Dickhaus1, Mutasim Abu Hasan2, Elizabeth Tremblay3, Kenneth Klinker4, Kenneth Rand5,6Stacy G. Beal51University of Florida College of Medicine, Gainesville, Florida, USA2University of Florida College of Medicine, Department of Pediatrics, Pediatric Pulmonary and Allergy Division, Gainesville, Florida, USA3UF Health Shands Hospital, Department of Infection Control, Gainesville, Florida, USA 4UF Health Shands Hospital, Department of Pharmacy Practice, Gainesville, Florida, USA 5University of Florida College of Medicine, Department of Pathology, Immunology, and Laboratory Medicine, Gainesville, Florida, USA6University of Florida College of Medicine, Department of Internal Medicine, Division of Infectious Diseases and Global Medicine, Gainesville, Florida, USA ABSTRACTObjective: Patients’ with cystic fibrosis respiratory systems become colonized with pathogens as early as the first year of life.  Some organisms are associated with a decline in pulmonary function and shortened survival, such as a mucoid strain of Pseudomonas aeruginosa (PA). Methods: We conducted a four year retrospective chart review study examining 158 pediatric and adult cystic fibrosis patients treated at an academic, tertiary care institution to compare patients treated by different antimicrobial regimens. Results: A higher proportion of mucoid PA study patients received alternate-monthly tobramycin therapy (83.3%), compared to those with non-mucoid PA (62.5%); although a large percentage of patients who had never had a mucoid PA infection were also receiving alternate-monthly tobramycin. Patients who had a mucoid PA infection had more hospitalizations and for longer periods of time than patients who had a non-mucoid PA infection; both mucoid and non-mucoid PA patients were hospitalized more often than patients who had never had a PA infection. We additionally found patients with mucoid PA infections to have strains that were either resistant or had intermediate resistance to tobramycin. Similar trends in resistance were not seen in patients who only received intermittent treatments with tobramycin. Conclusions Our findings on increased rates of infection with both Aspergillus (in the alternate-monthly inhaled tobramycin group) and NTM (in the overall patient population) comparative to international averages were also interesting, and open the doors to future research regarding CF patients with these infections. J Microbiol Infect Dis 2017; 7(4):178-185 Keywords:Cystic fibrosis, Pseudomonas, Tobramycin