Amphotericin B is a polyene antifungal agent, first isolated by Gold et al from Streptomyces nodosus in 1955. It is an amphoteric compound composed of a hydrophilic polyhydroxyl chain along one side and a lipophilic polyene hydrocarbon chain on the other. Amphotericin B has a high affinity for sterols, primarily ergosterols, of fungal and bacterial cell membranes. After binding to sterols, it forms channels in the membranes, causing small molecules to leak out. Amphotericin B induces K+ leakage which is separate from its lethal actionn, as was demonstrated in humna erythrocytes and is due to the inhibitory effect on the Na+/K+ pump. At sub-lethal concentrations, this agent stimulates ehther the activity of some membrane enzymes or cellular metabolism, in particular stimulation of some cells of the immune system. Amphotericin B is poorly soluble in water and now available in four formulations. The classic amphotericin B deoxycholate formulation has been available since 1960 and is a colloidal suspension of amphotericin B. A bile salt, deoxycholate, is often used as the solubilizing agent.
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