FDA Rationale for Breakpoints Recognition Decision for Disk Diffusion: Azithromycin and Neisseria gonorrhoeae

FDA has identified the disk diffusion inhibition zone diameters based on correlation with the FDA azithromycin minimum inhibitory concentration (MIC) breakpoints for Neisseria gonorrhoeae.  The reviewed materials included data used by the Clinical and Laboratory Standards Institute (CLSI) for establishing azithromycin disk diffusion breakpoints for Neisseria gonorrhoeae and the publication by Gianecini R et al. 2020 [1, 2].

In January 2025, FDA concluded that an azithromycin intermediate breakpoint of ≤1 mcg/mL and a resistant breakpoint of ≥ 2 mcg/mL are most appropriate for Neisseria gonorrhoeae [3]. Based on the review of available data, FDA identifies a disk diffusion resistant breakpoint of ≤ 26 mm and an intermediate breakpoint of ≥27mm.

1. Subcommittee on Antimicrobial Susceptibility Testing (AST) meeting minutes, January 2020.
2. Gianecini R et al. GASSP-AR Working Group; Galarza P. Testing of In Vitro Susceptibility of Neisseria gonorrhoeae to Azithromycin: Comparison of Disk Diffusion and Reference  Agar Dilution Methods. J Clin Microbiol. 2020 Oct 21;58(11):e01398-20.
3. FDA Rationale for Breakpoints Recognition Decision: Azithromycin and Neisseria gonorrhoeae.