In vitro interactions of antifungal agents against clinical isolates of Fusarium spp.

The in vitro activities of amphotericin B (AMB), itraconazole (ITC), voriconazole (VCZ) and terbinafine (TBF) alone and in the combinations AMB + VCZ, TBF + ITC and TBF + VCZ were evaluated against 29 clinical isolates of Fusarium spp. (15 Fusarium solani, 7 Fusarium oxysporum, 2 Fusarium decemcellulare, 2 Fusarium dimerum and 3 other Fusarium spp.). Minimum inhibitory concentrations were determined using the method of the Clinical and Laboratory Standards Institute and the interaction activity was calculated using the fractional inhibitory concentration index. The four antifungal drugs tested alone showed very limited activity against most of the isolates. In contrast, the combination TBF + VCZ showed synergy for 21 isolates. The combination AMB + VCZ showed synergism for only five strains. No interaction or antagonism was observed among the remaining strains. TBF + ITC showed no interaction for 18 strains. The in vitro antifungal activity of the drugs alone and in combination varied for different species. These results corroborate previous in vitro studies in which the combination TBF + VCZ showed synergy against Fusarium spp., although further studies are needed to elucidate its potential usefulness for therapy.