In vitro interaction of micafungin with conventional and new antifungals against clinical isolates of Trichosporon, Sporobolomyces and Rhodotorula.

OBJECTIVES The infections caused by basidiomycetous yeasts are often difficult to resolve. Combined therapy might be useful in those severe cases where a monotherapy was ineffective. The aim of this study was to evaluate the in vitro activity of combinations of micafungin with amphotericin B or fluconazole, itraconazole, voriconazole and ravuconazole against isolates of Trichosporon, Rhodotorula and Sporobolomyces. METHODS Twenty-seven clinical isolates were tested, i.e. 10 of Trichosporon asahii, two of Trichosporon mucoides, five of Sporobolomyces salmonicolor and 10 of Rhodotorula glutinis. Drug interactions were assessed by the chequerboard technique using the NCCLS microdilution method (M27-A2). The fractional inhibitory concentration index (FICI) was used to classify drug interactions. Results were interpreted as follows: synergy (FICI < or =0.5), no interaction (FICI >0.5 and < or =4.0), or antagonism (FICI >4.0). RESULTS Micafungin combined with amphotericin B showed the highest percentage of synergic interactions (78%) followed by micafungin/ravuconazole and micafungin/itraconazole (48% for each), and micafungin/fluconazole and micafungin/voriconazole (34% for each). Antagonism was not observed in any case. CONCLUSIONS Some of the combinations tested, especially micafungin/amphotericin B, have potential for the treatment of basidiomycetous yeast infections.