this is a potion, not a poison. you don't apply it using any rogue abilities. put it on your potion belt or make a hotkey or something and drink it to increase your poison resistance for a short time.
I just got one of these with a level fourteen rogue from doing the quests - it does list charges but cant get it to work at all - doesnt load in a slot either - dunno - broken??
Does it really work? Other people have said that the item does not trigger. In the picture, it doesn't say expendable, list charges, list an effect, or indicate that it's magic.