In vitro interaction between glabridin and voriconazole against Aspergillus fumigatus isolates.

BACKGROUND: Voriconazole (VRC) is widely recommended as the first-line therapy for invasive aspergillosis. However, surveillance studies have demonstrated that there is an increase in the frequency of azole resistance among Aspergillus fumigates isolates. In recent years, more studies on effective synergisms between natural agents and antifungal drugs have been published. AIMS: To evaluate the synergistic antifungal effect of glabridin (Gla) and VRC against A. fumigatus isolates. METHODS: Potential interactions between Gla and VRC were studied by using a microdilution checkerboard method based on the CLSI reference technique. To assess the interaction of drugs the fractional inhibitory concentration index (FICI) was calculated based on the Loewe Additivity model. RESULTS: The minimum inhibitory concentrations (MIC) obtained with Gla alone were relatively high (MIC50 16µg/ml). However, our results showed synergistic interaction between Gla and VRC against A. fumigatus strains, with FICI range values between 0.15 and 0.5. CONCLUSIONS: Synergistic activity of Gla and VRC against both VRC-sensitive and -resistant A. fumigatus isolates may lead to design new antifungal agents, especially for inhibiting those azole-resistant strains.