Amphotericin B liposomal microbiology
Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Ahmed Zaghw, M.D. [2]
Microbiology
Mechanism of Action
Amphotericin B, the active ingredient of AmBisome, acts by binding to the sterol component, ergosterol, of the cell membrane of susceptible fungi. It forms transmembrane channels leading to alterations in cell permeability through which monovalent ions (Na+, K+, H+, and Cl-) leak out of the cell resulting in cell death. While amphotericin B has a higher affinity for the ergosterol component of the fungal cell membrane, it can also bind to the cholesterol component of the mammalian cell leading to cytotoxicity. AmBisome, the liposomal preparation of amphotericin B, has been shown to penetrate the cell wall of both extracellular and intracellular forms of susceptible fungi.
Activity In Vitro and In Vivo
AmBisome has shown in vitro activity comparable to amphotericin B against the following organisms: Aspergillus fumigatus, Aspergillus flavus, Candida albicans, Candida krusei, Candida lusitaniae, Candida parapsilosis, Candida tropicalis), Cryptococcus neoformans, and Blastomyces dermatitidis.
Drug Resistance
Mutants with decreased susceptibility to amphotericin B have been isolated from several fungal species after serial passage in culture media containing the drug, and from some patients receiving prolonged therapy. Drug combination studies in vitro and in vivo suggest that imidazoles may induce resistance to amphotericin B. However, the clinical relevance of drug resistance has not been established.
Susceptibility Testing
Standardized methods of in vitro antifungal susceptibility testing have been developed for testing yeasts (1, 2, 3) and filamentous fungi (4, 5). The clinical relevance of the test results is not always clear.[1]
References
Adapted from the FDA Package Insert.