How would that work with the class special "Mettle"? As I recall it allows one with it to take half damage on a failed fort save. This would quickly reduce all poisons (at least a higher level) to a mere one point - presuming you follow the presumed rule of all damage having a minimum of one point (ie: the whole 'house cat can kill a commoner' bit).
Another idea is that if you succeed in your save the damage is put off for one minute. At that point you would make two saves - one for the original and one for the 'one minute later' bit (although I tend to think that it should be more variable than that). What happens upon the second save? Is it put off for yet another minute? If so, then how many times can the damage be put off?
Perhaps you could role the damage first. If there is only one point of damage and they succeed their save, they receive the point a minute later (the same time they make the second save, if there is one). If there is more than one point of damage, and they succeed their save, they take one point now and the rest is put off for a minute. If they succeed their next save then they take the next point and the rest is put off for yet another minute.
In this way the full damage is still received - even on a string of successful saves, but it is stretched out over several minutes, making it less damaging in the long run (as it is likely that by the time the brunt of the damage hits the encounter will have been long over - allowing others to use Heal checks to help them make their save, perhaps even negate their damage if, say, they beat the check by at least 10 points.
An Example of what I mean:
The PC is stabbed with a blade coated in poison (DC 19, 1d4 Con, 1d6 Con). The damage rolled is 2 Con. The PC makes the save and so only takes 1 Con damage. A minute later they make another save - and make it. As there is only one point of Con damage left, it is put off for one more minute. However, now they need to make the save for the 1d6 Con. Damage rolled is 4 Con. They again make their save and so only take 1 Con damage. Another ten rounds go by, but still a few remaining foes continue to attack. The PC makes their final save for the first Con damage, and they make it, so the last point of damage is averted. However, it is also time for the second roll for the d6 Con damage fort save. They make the roll, succeeding by 11 points and so take no damage. That point is effectively negated, leaving only two points remaing. Another minute, and this time the battle is over and another PC makes a Heal check to help them. The PC succeeds and so takes only 1 Con damage. Over the next two minutes two more checks are made, and both succeed, so the final point is also negated.
The final result? 3 Con damage taken over ~40 rounds. Note that if at any time the PC had failed their check they would have taken all remaining Con damage. So if the PC failed the initial save they would have taken 2 Con damage, and had they failed their 'minute later' save they would have taken 4 Con damage at that point. Similarly, note that 3 points were averted. Two were averted due to being the last point of damage and the PC making two successive succeeding fort saves to first delay and secondly overcome the damage. The third point was averted due to making a single spectacular save, beating the DC by 10 points.
This might make poisons both more realistic and potentially put more fear back into the PCs. Unless they have a good fort save and roll well they never know when the full brunt of the remaining poison damage will hit. Also, even if they make their save, unless there is only a single point of damage left they will still take one point of damage.
If you want, make it so that the save is made every round instead of every minute. Personally, I would add all the damage into a single pool and make the save every round or minute based on the type of poison. If the damage is in a single pool, then only one point may be resisted to the point of aversion (due to being the last point). Thus, in the example above, the PC would have had a pool of 6 Con damage and had to make a save every round to either put off most of it or take it all at once.
As for making the save every round, most combats do not last 10-20 rounds, let alone 20-30 rounds. As such, the 'benefit' of using poison on a weapon is typically only useful if the initial damage is notable (and in most it is the secondary damage that is most notable). So roll all damage at once, and make the save every round verse taking all damage or delaying most of it for a time. If multiple damage types exist (Str, Dex, Con, etc), then . . . I'm not sure. Perhaps take the first point of each pool at once, and continue as normal (ie: 4 Con, 3 Dex dmg, then the first round take 1 Con and 1 Dex if fort succeeds, or all if it fails, then the second round take 1 of each on success or remaining if fail, then finally take 1 Con and delay final Dex point on success or take all remaining on failure, then fourth round either delay last Con point on success or take remaining 2 Con, 1 Dex on failure, and final round take 1 Con on failure or no damage on success).
Anyway, I'm just brainstorming. What do you think? The damage is less, but it is also constant until all the poison has been resisted, and any chance failure could spell death due to massive ability damage if all ability damage is rolled in the first round and poolled. I imagine low fort save PCs (such as rogues) will be much more cautious and fearful of poisons, while higher fort save PCs will still be somewhat ambivalent to them but bothered by the constant drain - even on successful saves.
To make it more interesting, state that even ability damage - if poison based - might become ability drain. If a failure is made, roll an additional fort save for every ability damage received. Each additional failure makes that single point change to ability drain. For ability drain poisons, it increases the penalty to 2 drain instead of 1.
Makes Poison Immunity instead a +8 to poison checks. Thus they will almost certainly make their save, and often - but not always - they will succeed by enough to negate taking damage that round. At least for the lower level poisons. The higher level ones will still be problematic.
