I think it should be a high DC, so it'd be more threatening against high level players. Who also have the resources for antidotes. If it's a low DC, it'll only be effective against low levels, who are less likely to have antidotes. Maybe make the DC based off herbalism skill.
I'd like it if it was a more threatening than a typical NWN poison as well. Stat damage only harms you in a dungeon, it's an inconvenience outside of dungeons.