Background: Sitafloxacin is a newly approved oral fluoroquinolone in Thailand for treatment of respiratory tract and urinary tract infections. Initial in vitro susceptibility testing showed its effect on Escherichia coli with extended-spectrum betalactamases (ESBL), Klebsiella pneumoniae with ESBL, Pseudomonas aeruginosa, and carbapenem resistant Acinetobacter baumannii.
Objective: To retrospectively review in vitro susceptibility to sitafloxacin on clinical isolates from HRH Princess Maha Chakri
Sirindhorn Medical Center, Srinakharinwirot University (SWU) and Samitivej Sukhumvit Hospital (SVH).
Material and Method: Between January 2014 and June 2015, all clinical isolates from SWU and SVH that were added to test
in vitro susceptibility to sitafloxacin were included in the present study. The susceptibility for sitafloxacin was identified by disk
diffusion method with inhibition zone diameter 19 mm or greater, considered to be sensitive, and smaller than 16 mm
considered to be resistance. The comparative activities of sitafloxacin to other antibiotics were determined by organisms. All bacteria with count numbers of more than 30 would be shown in results.
Results: Among 1,288 clinical isolates from 1,163 clinical specimens that were added in vitro susceptibility test to sitafloxacin, there were 728 clinical isolates from SWU and 560 clinical isolates from SVH. The most common specimens were sputum (482), urine (385), pus (96), and blood (81). Organisms with comparative activities included E. coli, K. pneumoniae, P. aeruginosa, A. baumannii, and Stenotrophomonas maltophilia. The susceptible percentage of sitafloxacin was 72.69% for all E. coli (n = 216) (68.26% for E. coli with ESBL and 86.96% for E. coli without ESBL), 39.31% for all K. pneumoniae (n = 173) (50% for K. pneumoniae with ESBL, 61.11% for K. pneumoniae without ESBL and 13.11% for carbapenem resistant enterobacteriaceae (CRE) strain of K. pneumoniae), 60.66% for P. aeruginosa (n = 366), 66.32% for A. baumannii (n = 386) and 93.94% for S. maltophilia (n = 33). Sitafloxacin had more susceptible percentage as compared to ciprofloxacin for all strains of E. coli, K. pneumoniae, P. aeruginosa, and A. baumannii and more susceptible percentage as compared to levofloxacin for S. maltophilia. Although sitafloxacin might not have good activity against CRE strain of K. pneumoniae, at least some (13.11%) were susceptible as compared to 0% for ciprofloxacin.
Conclusion: Sitafloxacin had more susceptible percentage to E. coli, K. pneumoniae, P. aeruginosa, A. baumannii, and S. maltophilia compared to comparative fluoroquinolones. It should be considered an antibiotic for treatment of respiratory
tract and urinary tract infections caused by the resistant strains of these bacteria with susceptible proven of in vitro susceptibility.

Keywords: Sitafloxacin, Comparative in vitro susceptibility, Fluoroquinolones