Evaluation of antifungal effects of terbinafine and itraconazole using neutral red staining.

Neutral red staining is a newly described method for evaluating the viability of fungal cells. Using this method, the antifungal effects of terbinafine and itraconazole were evaluated in vitro. When the number of neutral red-positive Trichophyton mentagrophytes conidia treated with these two oral antifungals was compared with the number of culture-proved viable T. mentagrophytes conidia, a strong positive correlation was found. This result confirms that neutral red staining is a useful method for evaluating the viability of T. mentagrophytes in vitro, and that it can be used for the evaluation of antifungal activity. We conclude that the effectiveness of an antifungal drug should not be evaluated by direct microscopic examination alone, but with the additional aid of mycological culture or neutral red staining.