Yep, certain medical items can be used to treat fish for things like severe bacterial infections. Some anti-biotics and other such things are also used as there are some cases where fish medication just does not have that 'kick' to get rid of it.
I doubt anyone would, you would think they would use similar stuff in fish medicine if needed, right? I think it has something to do with the legality/price/license needed to obtain and use such ingredients.