It depends if the rat poison is already in the rat or not. If it is in the rat and you cook the rat, then the poison will be negated. If you don't cook the rat then raw rat will see you off in 15 hours 12 minuets and 8 seconds, approx.
Waferin which is rat poison is used to thin the blood of heart patients, so actually it will prolong your life. If you want, I'll send you some of my ex-wifes gravy, that should do it for you.
you need to eat quiet a lot of poison for it to do any damage! Depending on the exact poison the anitdote is simply a shot of vitamin k1... eat lots of maize!