ANTIFUNGAL AND ANTIVIRAL AGENTS
lies the problem: anything that damages fungal cells is likely to damage human cells too.
Polyene antibiotics such as amphotericin and nystatin (both produced by species of Streptomyces) act on the sterol components of membranes; their use is limited, because human cells can also be affected by their action (to use a term we learnt earlier in this chapter, they have a low therapeutic index). Nystatin is used topically against Candida infections, while amphotericin B is generally used against systemic infections of fungal origin. The latter substance can have a wide range of serious side-effects, but in some cases infections are so severe that the physician is faced with no alternative. Synthetic compounds such as the imidazoles have a similar mode of action to the polyenes; they are effective against superficial mycoses (fungal infections of the skin, mouth and urino-genital tract). Griseofulvin, a natural antibiotic produced by a species of Penicillium, is another antifungal agent whose use is restricted; it works by interfering with mitosis and not surprisingly has a range of side-effects. Although used to treat superficial infections, it is taken orally.
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