Drug Interaction Assay

A checkerboard microdilution method (Pillai et al., 2005) was used to examine interactions between itraconazole and H3, using four isolates from each species in the yeast form. Itraconazole and H3 were tested at concentrations of 0.06–4 mg/L and 0.03–0.5 mg/L (in serial 1:2 dilutions), respectively, against final yeast concentrations of 0.5–2.5 × 10³CFU/mL at 35°C for 5 days. Antifungal combinations were classified according the fractional inhibitory concentration index (FICI), defined by the equation: FICI = (MICa in combination/MICa tested alone) + (MICb in combination/MICb tested alone), where “a” was itraconazole and “b” was H3 (Pillai et al., 2005). Interactions were considered synergistic if FICI ≤ 0.5, absent if FICI >0.5 and ≤ 4, and antagonistic if FICI >4 (Odds, 2003).