Which drug is classified under the polyene antifungal class?

Amphotericin B is classified under the polyene antifungal class, making it the correct choice. Polyenes are a group of antifungal agents that are characterized by their ability to bind to ergosterol, a key component of fungal cell membranes. This binding disrupts the integrity of the cell membrane, leading to cell death.

Amphotericin B is particularly effective against a variety of fungal infections, including those caused by Candida species and Cryptococcus neoformans. Its broad spectrum of activity and mechanism of action make it a cornerstone in treating serious systemic fungal infections.

The other options represent different classes of antifungal agents. Flucytosine is an antimetabolite that interferes with fungal nucleic acid synthesis, Itraconazole is an azole antifungal that inhibits ergosterol synthesis, and Caspofungin is an echinocandin that disrupts the synthesis of the fungal cell wall. Each of these agents has a unique mechanism of action and is used for specific types of fungal infections, but none of them fall under the polyene classification.