Interpretative criteria for the agar diffusion susceptibility test with azithromycin

Abstract
Azithromycin (CP-62,993) is a macrolide with a tendency to concentrate in various body tissues. Difficulties that arise when establishing tentative minimum inhibitory concentration (MIC) breakpoints for such a drug include the question of whether MICs should be compared with the achievable concentrations in blood or in tissue. Pending clinical experience with this drug, we recommend the following tentative criteria for interpreting tests with 15 μg azithromycin discs: susceptible ≥18 mm (MIC ≤2mg/l) and resistant ≤13mm (MIC ≥ mg/l).