In Vitro Evaluation of Combination Antifungal Activity against Fusarium Species Isolated from Ocular Tissues of Keratomycosis Patients

Purpose To determine the minimum inhibitory concentrations (MICs) of five antifungal agents against Fusarium species isolated from ocular tissues and to evaluate anti-Fusarium species activities of eight combination treatments in vitro. Design Experimental research. Methods Thirty-eight isolates of Fusarium species were collected from patients' ocular tissues and were cultured in vitro. The MICs of natamycin, terbinafine, itraconazole fluconazole, and amphotericin B, either used alone or combined with other compounds, were evaluated by checkerboard microdilution technique based on the Clinical Laboratory Standards Institute proposed standard. The interactions were assessed using the Fractional Inhibitory Concentration Index model. Results In the MIC study, the MIC90 of each drug used alone were: natamycin, 16 μg/ml; terbinafine, 8 μg/ml; itraconazole, >16 μg/ml; fluconazole, >64 μg/ml; and amphotericin B, 4 μg/ml. Synergism was obtained in the amphotericin B plus terbinafine (81.6%) group and in the amphotericin B plus itraconazole (84.2%) group, with an obviously decreased MIC value of amphotericin B. Antagonism was shown in the natamycin plus azoles and in the natamycin plus terbinafine groups in 52.6% to 60.5% of Fusarium species strains. Conclusions Amphotericin B plus terbinafine or itraconazole demonstrated more effective anti-Fusarium species activity than single-use in vitro treatment, which implies that these combinations may be helpful in treating fungal keratitis. The combinations of natamycin plus azoles or natamycin plus terbinafine were not satisfactory and can be avoided. Further in vivo studies are needed to elucidate the potential usefulness of these combination therapies.