Key issues concerning fungistatic versus fungicidal drugs.

Are there any fungicidal drugs available today? A critical issue in answering this question is that of definition. The simplest, most stringent definitions identify fungistatic drugs as those that inhibit growth, whereas fungicidal drugs kill fungal pathogens. The immunocompetent host is usually far better equipped to eliminate fungal pathogens than the immunosuppressed host. Therefore, it would be especially desirable to have a truly fungicidal drug, one that absolutely kills and fungi, as a treatment option for the immunosuppressed patient. The critical question would be whether a fungicidal drug can be delivered to the target site in a concentration high enough for a sufficient time to reduce the intralesional fungal counts to zero. By this simple definition, there are no fungicidal drugs available today. However, an accepted alternative definition is that often used by the bacteriologist: Fungicidal drugs are those that lead to a reduction of 99.9% of the initial inocula. Although this less restrictive in vitro standard is more easily met, it has serious limitations. Whether the 99.9% kill should be an acceptable standard remains uncertain. As an alternative, the minimum inhibitory concentration, though indicating static activity, has served well; perhaps it should be the only information reported for fungal susceptibility testing.