Poisons don't work the way it sounds like you are describing. You don't apply them to your weapon and they work for a certain time. You equip them and they work like an enchant, procing 20% of the time on light/heavy attacks and weapon abilities, until you run out or unequip them.
Poison Tracker will show how many of the equipped poison you have left and shows an indicator when they proc. Poison Master (see my sig) will let you hotkey poisons to easilly equip/unequip them on demand.
So long as you have a poison equipped on a weapon, that weapon's enchants will not work.