As for it being fatal, I think the only reason they are saying it's fatal, because they don't know what exactly it is. I've come to understand that Treatment A work for Poison A, but Treatment A for Poison B will either not work, or just kill you on the spot (Well, maybe not quite on the spot, but...).
The doctor clearly said it was a "ricin-based" poison. Given what the link above says about ricin in real life, I would imagine that anything ricin-based would have pretty much the same effects and the same treatment, at least for a given method of exposure. But as I said, this show has often played fast and loose with the facts. For the purposes of the story, this "ricin-based toxin" will work however they want it to, regardless of what happens in real life.