Bring an Undamaged Venom Sac to Apothecary Lydon in Tarren Mill.
I must have a fresh sample of the venom you brought me. The spiders from which it was gathered must dwell in the Hinterlands -- hunt them until you find an undamaged venom sac and bring it to me. You will find many spiders near the troll city of Shadra'Alor.
Do not tarry, [player], for the venom sac must be fresh when you deliver it.