Find Kor'ghan in Orgrimmar and get the Venomtail Antidote. Then bring the antidote to Rhinag near the northwestern border of Durotar.
[player]... your timing is perfect. I just hope I can compliment your haste as well.
I was careless while fighting a few of the venomtails nearby, and one of them stung me deeply. I can feel its poison weakening me even as we speak. At this rate, I got maybe an hour left to live. But I'll need your help if I'm to do so...
Kor'ghan in Orgrimmar knows how to make the antidote. Find him... and hurry, [player]. I won't be able to last much longer. He should be in the Cleft of Shadow.