There's three variant poison rules in the original, level based, luck based, and Con based, depending on if you wanted 50th level creatures able to drink vats of cyanide, or you wanted dwarves drinking cyanide, or you wanted anyone drinking cyanide to be at risk of dying.
Level based had the issue of high levels resisting too easy.
Con based had the issue of high cons resisting too easy.
Luck based put everyone on a level playing field with more or less equal chances.
The downside, as you go more realistically toward "Posion at X dose kills you, period" keep in mind that means it will become far more common as a way to deal with high level foes. . .like when your 20th level PC gets taken out by a poison dart, or the PCs kill your 50th level dragon with a poison arrow.
It's not necessarily a problem as long as you want that feel, but keep in mind that being engulfed in a ball of super hot fire or taking a clean shot with a weapon should also realistically just kill you too every time, and few people advocate things like "Nobody can purchase more than 4 ranks of body development" or "Everyone resists all spells at 1st level". . . .either of which fit into the same logic of "realistically you can't make yourself more fire resistant/stab resistant/etc resistant" either.