Say you are attacked and get poisoned by a spider on its turn. You immediately make a Fort save to resist the poison.
If the poison has a duration, do you make subsequent saves on the spider's initiative or your own?
If you save on your own turn, does that mean you can be affected twice in the same round by the poison? (i.e., if the spider acts first in the round you save on its initiative and then on your own)
If you save on the spider's turn, how does that work if the spider hit you with an Attack of Opportunity? (i.e., not on its initiative count)
It's on your turn. If the spider had higher initiative, you make the first save on its attack, then on subsequent combat rounds, you save on your turn.
Check the bottom of this page:
http://www.d20pfsrd.com/gamemastering/afflictions/poison
Thanks! That's very helpful.