2.5. Calculation of the Fractional Inhibitory Concentration (FIC) Indexes and Evaluation of Drug Interactions

To evaluate drug interactions, the FIC indexes were calculated. The FIC index of the antifungal drugs (drugs A and B) was calculated using the following formula: (MIC of A in combination with B/MIC of A alone + MIC of B in combination with A/MIC of B alone) [21,22]. The interaction was considered synergistic if the FIC index was ≤0.50, additive if >0.50 but <1.0, indifferent if ≥1.0 but ≤2.0, and antagonistic if >2.0 [22].