IN-VITRO SUSCEPTIBILITY TESTING OF MALASSEZIA-FURFUR AGAINST RILOPIROX

The in vitro antifungal activity of the new hydroxypyridone antimycoti c rilopirox has been evaluated against 29 separate clinical isolates o f Malassezia (M.) furfur obtained from patients with pityriasis versic olor, seborrhoeic dermatitis or dandruff. Minimum inhibitory concentra tions (MICs) of rilopirox were measured by the agar dilution technique and, in comparison, by a recently described microdilution method with colorimetric detection of the MIC end points. Rilopirox was found to be able to inhibit growth of all clinical yeast isolates. For the inve stigated M. furfur strains MIC values from 12.5 to 50 mu g ml(-1) with a median of 25 mu g ml(-1) were determined by the agar dilution metho d. Using the microdilution technique, MIC values between 16 and 128 mu g ml(-1) (median 32 mu g ml(-1)) were found for the M. furfur isolate s. It has to be taken into account that with a 0.3% solution concentra tions of 300,000 mu g ml(-1) are applied to the skin. Furthermore, due to its extreme low penetration rilopirox is long-term available in th e skin in inhibiting concentrations. In comparison with rilopirox, the in vitro susceptibility of M. furfur against the systemically applica ble triazole antimycotic itraconazole and clotrimazole, an established topical antifungal, was tested. As expected, low MIC values for these azoles were found by the agar dilution method. The median of the MIC of M. furfur was 0.1 mu g ml(-1) for itraconazole, and 6.25 mu g ml(-1 ) for clotrimazole. The inhibitory effectivity of rilopirox against cl inical isolates of M. furfur seems to justify its therapeutic evaluati on in clinical trials. This new antifungal may be a useful alternative not only in pityriasis versicolor but also in seborrhoeic dermatitis due to the growth inhibition of M. furfur.