In vitro activity of fluconazole, itraconazole, voriconazole and terbinafine against fungi causing onychomycosis

Background. Onychomycosis is one of the commonest dermatological diseases worldwide. The antifungal activity of current medications varies, and treatment failure occurs in 25-40% of treated patients. Aims. To evaluate the in vitro antifungal activity of itraconazole, fluconazole, terbinafine and voriconazole against isolates taken from patients with onychomycosis. Methods. Nail isolates were evaluated according to methods described in the protocols of the Antifungal Susceptibility Testing Subcommittee of the European Committee on Antimicrobial Susceptibility Testing (AFST-EUCAST) and the Clinical and Laboratory Standards Institute (CLS M38-A), and a CLSI M38-A modified technique for dermatophytes. Antifungal agents tested included terbinafine, itraconazole, voriconazole and fluconazole. Results. In total, 103 isolates of Candida species (n = 58), Fusarium species (n = 10), Fusicoccum dimidiatum (n = 4), Scytalidium hyalinum (n = 1) and dermatophytes (n = 30) were evaluated. Itraconazole and voriconazole were the most active agents against Candida species, whereas terbinafine and voriconazole were most potent against dermatophytes. Fusarium species had the highest minimum inhibitory concentration (MIC) values with all antifungal agents. Conclusions. The aetiological agents of onychomycosis that we found differ from those found in other countries, suggesting that the heat and humidity of the Colombian climate could favour yeast nail infections. The lowest MICs for Candida species (obtained with voriconazole, followed by itraconazole) may be explained by emerging resistant strains. Against dermatophytes, the lowest MICs were obtained with terbinafine, followed by voriconazole. MIC values for the evaluated agents were higher for non-dermatophyte filamentous fungi than for other fungi. As MIC breakpoints have not yet been established for onychomycosis therapies, it remains unclear if in vitro activities of antifungal drugs are predictive of clinical outcome. Well-designed clinical studies are necessary to assist clinicians in choosing the best antifungal agents.