The basic antodote needs 8 seconds to work - hell thats nearly the whole time the poison will work. It gets better with Advanced and Concentrated, with 4 and 2 seconds to work.
But:
-) It also adds to your drug flash as far as I know.
-) With Concentrated Antidote you remove 1 Stack. 1000 NC to remove 1 Stack of damage. Granted, sometimes the damage is very high that you remove with that, but do you know how often you can get that stack? It literally burns through your money if you want to use it.
-) You cannot recycle it into more, although it is no faction item. As is the case with the basic resist potions.
I know they play into balancing, so I guess its not so easy to decide, but I think a bit of improvement could be done to them later or sooner.
-) If they were recycleable, it would be justified to go through them at some rate.
-) If they had more than one use their price would be justifierd more, and you wouldn't have to carry a whole tank of them around with you for them to be useful, cause you could make them when you need them (they being sold only with a few traders doesn't help, though its quite nice to find them)
-) If they removed more than one stack it would also make them more useful (for example time being always fast, but different amount of stacks removed between basic, advanced and Concetrated)
To clarify: I do not say to implement all of these at once, just pick one or two, or combine them. I just think they should be a bit more useful, not a complete need-to-have-make-all-easy-tool.