Amphotericin B is a polyene antibiotic isolated from Streptomyces nodosus . It contains a macrolide ring and an aminosugar, mycosamine. It is extremely unstable in solution, particularly in normal saline. It forms a channel through the membrane that allows the passage of potassium and other small molecules. The fungus is unable to maintain its internal environment.
Resistance is rare and slow to develop.
The drug crosses cell membranes very poorly, therefore, it is poorly absorbed from the gut and has poor penetration into the eye, CSF, and joint capsules. For treatment of meningitis, it must be given intrathecally. It is given only via IV injection or intrathecally. Some authorities feel its topical use is no longer justified because of the availability of superior products. The drug has MANY adverse effects, some serious.