The in vitro antifungal activity of the new hydroxypyridone antimycotic
rilopirox has been evaluated against 38
fluconazole-susceptible and -resistant clinical isolates of Candida albicans together with other Candida species isolated from patients with human immunodeficiency virus (
HIV) infection and oropharyngeal candidosis. Minimum inhibitory concentrations (MICs) of both
rilopirox and
fluconazole were measured by a microdilution method using high-resolution medium supplemented with
asparagine and
glucose at pH 7.0. In comparison, an
agar dilution technique was carried out for susceptibility testing of the
antifungal agents.
Rilopirox was found to be able to inhibit growth of all clinical yeast isolates. The
rilopirox MICs at which 50% and 90% of strains were inhibited (MIC50 and MIC90 respectively), as determined by the microdilution method, were 4 and 8 micrograms ml-1 respectively. The highest MIC values for
rilopirox using microdilution and the
agar dilution method were 32 or 25 micrograms ml-1 respectively. On the other hand, for
fluconazole, the MIC50 and MIC90 achieved were 0.5 and 128 micrograms ml-1, respectively, which means that the MIC90 value of
fluconazole was 16-fold higher than that of
rilopirox. Using the
agar dilution technique, the MIC values of
rilopirox were in the range 0.006-25 micrograms ml-1 with a median of 3.12 micrograms ml-1. For
fluconazole, the MIC90 value was four-fold higher than that for
rilopirox, indicating a considerable proportion of yeast strains with high MICs of 100 micrograms ml-1, suggesting in vitro resistance to this
azole antifungal. All strains with diminished
fluconazole susceptibility were susceptible to
rilopirox. Even Candida krusei and Candida glabrata exhibited good in vitro susceptibility to
rilopirox. Therefore, this new
antifungal agent may be used as an alternative not only in the treatment of vaginal candidosis, but also in oropharyngeal
Candida infections, e.g. in
AIDS patients.