Amphotericin B is an antibiotic that fights fungal infections in the body. Amphotericin B is used to treat serious, life-threatening fungal infections. It is not for use in treating a minor fungal infection such as a yeast infection of the mouth, esophagus, or vagina. Amphotericin is usually given after other antifungal antibiotics have been tried without successful treatment of symptoms. Amphotericin B may also be used for other purposes not listed in this medication guide.