Objective: To investigate the in vitro activity of sitafloxacin compared to that of ceftriaxone, cefixime, and ciprofloxacin against Neisseria gonorrhoeae isolated from Thai patients.

Materials and Methods: Antimicrobial susceptibility testing of ceftriaxone, cefixime, ciprofloxacin, and sitafloxacin in 52 strains of N. gonorrhoeae isolated from Thai patients was performed by disk diffusion method and agar dilution method to determine the inhibition zone diameters and minimum inhibitory concentrations [MICs] of ceftriaxone, cefixime, ciprofloxacin, and sitafloxacin.

Results: All N. gonorrhoeae isolates were susceptible to ceftriaxone (MIC ≤0.025 mg/L, zone diameter ≥35 mm) and cefixime (MIC ≤0.025 mg/l, zone diameter ≥31 mm). All N. gonorrhoeae study isolates were resistant to ciprofloxacin (MIC ≥1 mg/l, zone diameter ≤27 mm). The inhibition zone diameters of sitafloxacin against N. gonorrhoeae study isolates were 41 mm or more in 35 isolates (67%), and ranged from 28 to 40 mm in 17 isolates (33%). When the interpretative inhibition zone diameter of resistance to ciprofloxacin (27 mm or less) was applied to sitafloxacin, no N. gonorrhoeae study isolates were considered resistant to sitafloxacin. The MIC₅₀ and MIC₉₀ of sitafloxacin against N. gonorrhoeae study isolates was 0.06 and 0.12 mg/L, respectively. When the interpretative MIC of ciprofloxacin resistance (more than 1 mg/L) was applied to sitafloxacin, no N. gonorrhoeae study isolates were considered resistant to sitafloxacin.

Conclusion: Sitafloxacin is active against ciprofloxacin-resistant N. gonorrhoeae. A clinical study in sitafloxacin therapy to treat gonococcal urethritis caused by ciprofloxacin-resistant N. gonorrhoeae should be considered.

Keywords: In Vitro Activity, Neisseria gonorrhoeae, Sitafloxacin, Fluoroquinolone