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Pharmacology: Nystatin exerts its antifungal activity by binding to sterols in the fungal cell membrane. The drug is not active against organisms (e.g., bacteria) that do not contain sterols in their cell membrane. As a result of this binding, the membrane is no longer able to function as a selective barrier, and potassium and other cellular constituents are lost.
Pharmacokinetics: Nystatin is poorly absorbed from the gastrointestinal tract, and detectable blood concentrations are not obtained after usual doses. Following oral administration, nystatin is excreted almost entirely in feces as unchanged drug. The drug is not absorbed from intact skin or mucous membranes.
Microbiology: Spectrum: Nystatin has fungistatic or fungicidal activity against a variety of pathogenic or nonpathogenic yeasts and fungi. In vitro, nystatin concentrations of approximately 3 μm/mL inhibit Candida albicans and C. guilliermondi. Concentrations of 6.25 μg/mL are required to inhibit C. krusei and Geotrichum lactis. It is also effective against Aspergillus spp., Coccidioides immitis, Cryptococcus neoformans, Histoplasma, Capsulatum, Blastomyces dermatidis, and other yeasts and fungi. In general, there is little difference between minimum inhibitory and fungicidal concentrations for a particular organism. Nystatin is not active against bacteria, protozoa, or viruses.
Resistance: Candida rarely becomes resistant in vivo. When resistant strains appear, they frequently are also resistant to other polyene antifungal antibiotics.
