In vitro combined effect of ceftriaxone and azithromycin against Neisseria gonorrhoeae

Objective To investigate in vitro combined effect of ceftriaxone and azithromycin against clinical isolates of Neisseria gonorrhoeae (NG) . Methods A total of 25 NG clinical isolates were collected from the STD clinic of Dalian Dermatosis Hospital in 2012. Epsilometer test (Etest) method was used to determine the minimum inhibitory concentrations (MICs) of ceftriaxone and azithromycin against NG isolates. Fractional inhibitory concentration index (FICI) was calculated to evaluate the in vitro combined effect of ceftriaxone and azithromycin against NG isolates. Results The mean MICs of ceftriaxone and azithromycin were 0.032 mg/L (range, 0.008-0.064 mg/L) and 0.834 mg/L (range, 0.064-4.000 mg/L) , respectively. The FICI ranged from 0.724 to 2.696, and ceftriaxone and azithromycin showed an additive effect against the above NG isolates. Conclusion Ceftriaxone and azithromycin show an additive effect against NG in vitro, but further studies with large sample size are needed to confirm their effects. Key words: Neisseria gonorrhoeae; Ceftriaxone; Azithromycin; Drug interactions