I don't know if antidote works on lycanthropy though.
I'm not entirely sure, but my guess is no (at least not when already polymorphed). I got lycanthropy from the fountain, drank the antidote and got a message "Aaah... you feel much better."
But then, around the wolf level, I changed into a werewolf, so I must have either caught it again or it never gone away. I drank the antidote again when in werewolf form, and there was no effect.
(although the potion was split into two cans, so that may have something to do with it)