IMO the saves would get harder to resist the more they body has to fight off. I would probably give it a -5 tp -50 per exta does depending on the poisons severity.
Also IMO the more the is it might be easyer to smell, tast, see but only if the is in the description on the posion.
MDC
Edit:
I might also check a toxicology book to see if thier is any info on poison. Or ask your doctor the next time you visit.
MDC