Kitten

The amount to poison a wound would imply the damn blade is dripping streams of poison. If it's been coated in it, it will dry and degrade with the oxygen in the air, eventually becoming a weak poison and giving the victim a stomach ache or intoxication at best.

tl;dr If you're going to coat your weapon in poison, make sure it's a magical poison. ^^

Do it like Cyndikate does it. Carry around ***** syringes/needles and like 50 different things to put in them and inject people with it on a whim.