That poison indeed has no antidote.
Because this poison was made for Baron Stuart, and for revenge against the Stuart Family!
When developing this poison, there was never any intention of creating an antidote. Billy Blossom even feared that he might act emotionally. During the development of the poison, he deliberately had the most dangerous ingredient hidden by those working on it, unknown to anyone.
As such, it would be nearly impossible for the two brothers to develop an antidote.
By doing this, the poison was meant to kill Baron Stuart once and for all, with no medicine on Earth to cure it. It would plunge the Stuart Family deep into despair, letting them taste the helplessness of losing a loved one, unable to do anything but watch him die slowly - this would be even more pleasurable than killing their entire family and crushing their corporation!
Hearing this, Baron Stuart's brow furrowed involuntarily.
"What did you say?"