Micafungin in combination with voriconazole in Aspergillus species: a pharmacodynamic approach for detection of combined antifungal activity in vitro

Abstract

Preclinical and clinical evidence indicate that echinocandin-triazole combinations provide enhanced killing versus triazoles alone against some Aspergillus isolates, however, in vitro test results designed to detect this combined effect are difficult to interpret. We used a straightforward pharmacodynamic approach based on a microdilution format and a colorimetric analysis to harmonize growth end points. We detected a fourfold decrease in the EC90 of voriconazole when tested in combination with micafungin (4 mg/L) against isolates of Aspergillus fumigatus and Aspergillus terreus, but not against an isolate of Aspergillus flavus. Echinocandin-enhanced voriconazole activity was confirmed in A. fumigatus and A. terreus but not A. flavus by fluorescent morbidity staining and fluorescence microscopic analysis of damaged hyphae. A microdilution-based pharmacodynamic method for testing antifungal combinations provides a less ambiguous description of the combined effects of antifungals against moulds and could be useful in reference laboratories that routinely evaluate the activity of antifungal combinations in vitro and in vivo.