Azithromycin and erythromycin resistant Neisseria gonorrhoeae following treatment with azithromycin.

A pre-treatment and a 3-week post-treatment isolate of Neisseria gonorrhoeae from a 13-year-old boy treated with azithromycin in a single 1 g oral dose were characterized microbiologically. Both isolates were of the same serovar/auxotype (1B6/non-requiring) and had similar antibiograms apart from erythromycin and azithromycin: the pre- and post-treatment MICs (minimum inhibitory concentrations) were: 1 mg/L and 32 mg/L to erythromycin and 0.125 mg/L and 3 mg/L to azithromycin. The finding that both isolates were 1B6/NR, had similar antibiograms (other than azithromycin and erythromycin), and no other 1B6/NR isolates were resistant to erythromycin supports the view that macrolide resistance developed following treatment. A high overall level of azithromycin susceptibility was confirmed by testing 67 clinical isolates: MIC90 0.5 mg/L (range 0.023-0.75 mg/L). We conclude that the long half-life of azithromycin which is beneficial in treating chlamydial infection may result in increased selective pressure for resistance in gonococci. This report also highlights the importance of antibiotic susceptibility surveillance of gonococci and stresses the need for appropriate treatment of gonococcal infection, particularly when it is prescribed outwith departments of genitourinary medicine.