Bring Faranell's Parcel to Master Apothecary Faranell in the Undercity.
The venom you gathered from the Witherbark's spider god is quite a find! I've been able to kill nearly two dozen rabbits with just a drop of the stuff. Granted, some of those rabbits were very young and small enough to fit in the palm of one's hand so I'm certain their resistance to toxins was low, but it can't be denied that this poison is powerful!
I'd like a sample sent to my superior, Apothecary Faranell in the Apothecarium of the Undercity. I am positive he would want to test this himself.