Amphotericin B is an antifungal medication used for serious fungal infections and leishmaniasis. The fungal infections it is used to treat include mucormycosis, aspergillosis, blastomycosis, candidiasis, coccidioidomycosis, and cryptococcosis. For certain infections it is given with flucytosine. It is typically given intravenously (injection into a vein).

Common side effects include a reaction with fever, chills, and headaches soon after the medication is given, as well as kidney problems. Allergic symptoms including anaphylaxis may occur. Other serious side effects include low blood potassium and myocarditis (inflammation of the heart). It appears to be relatively safe in pregnancy. There is a lipid formulation that has a lower risk of side effects. It is in the polyene class of medications and works in part by interfering with the cell membrane of the fungus.

Amphotericin B was isolated from Streptomyces nodosus in 1955 at the Squibb For Medical Research Institute from cultures isolated from the streptomycete obtained from the river bed of Orinoco in that region of Venezuela and came into medical use in 1958. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication.