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Compared with antibacterial agents, relatively few antimicrobials are available for treatment of fungal infections. Many substances with antifungal activity have proved to be unstable, to be toxic to humans, or to have undesirable pharmacologic characteristics, such as poor diffusion into tissues. Of the agents in current clinical use, the newer azole compounds have the broadest spectrum with significantly lower toxicity than earlier antifungal agents. An even newer class of cell wall active agents offers hope for the selective toxicity that β-lactams provide for antibacterial therapy.
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Many antifungals are too toxic for use
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Fortunately, most fungal infections are self-limiting and require no chemotherapy. Superficial mycoses are often treated, but topical therapy can be used, thus limiting toxicity to the host. The remaining small group of deep mycoses that are uncontrolled by the host's immune system require the prolonged use of antifungals. This, combined with the fact that most of the patients have underlying immunosuppression, makes them among the most difficult of all infectious diseases to treat successfully. The characteristics of currently used antifungal agents are discussed next and summarized in Table 44–1. They are discussed in the text that follows in relation to their target of action, as illustrated in Figure 44–1.
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