Antifungal susceptibility testing of dermatophytes

In order to help guide treatment, antifungal susceptibility testing is often performed in clinical microbiology laboratories. The results of these in vitro assays are used by clinicians to change therapy should resistance be detected, continue with current regimens with susceptible results, and as an aide in determining possible reasons for treatment failure. Antifungal susceptibility testing can be performed against dermatophytes, although fewer assay formats are recommended for these types of fungi compared to yeasts and molds. In addition, clinical breakpoints and epidemiologic cut-off values are not currently available for dermatophytes to help with the interpretation of these results. However, recently studies have demonstrated that reduced in vitro susceptibility to terbinafine, an allylamine commonly used in the treatment of dermatophyte infections, may be associated with clinical failures.