poisen annihilates poisen.

your body will extract poisen by itself, (kidneys etc.)

give me an example of the situation, i'm not quite sure what scenario you have in mind.

its entirely possible

you have to understand what makes something poisonous; its catalyzing an unwanted chemical reaction in the body which is harmful / deadly. The goal would be to design a medecine or something that will neutralize the poison before it overwhelms the bodys natural detoxification abilities

now as to which specific toxins, idk. theres a lot involved. Amount, potency, time taking medecine, etc etc.

enzymes catalyse chemical reactions. once you are poisoned, you'll get a fever, why?
because your enzymes can only work in a specific temperature in humans 36.5-37.5.
fever is a defence mechanism of our body, which will increase the temperature of the body.
this will cause the enzymes to denature and decrease the rate of chemical reactions, hence the effect of poison is reduced. your kidneys will then extract the poison from your body. sweating is also a way to extract it.

i don't think that there is medicine which will actually help you to get rid of the poison, since your body will do this on its own anyway.
however there should be medicine which will help your body to do this action, and or reduce the effectiveness of the poison.

transfusion.

well thats not technically a medecine

heavy metal poisoning treatments use medicine to detoxify the body..

it all depends on what the "poison" is because different treatment possibilities.

he asked how they extract it.

why does everyone spell medicine funny? is it a UK thing or something?

That's actually really cool.

usually your body itself will get rid of the psn. If someone got psn in themselves, medicine focuses more on blocking the psn's effect rather then get rid of it which the body does automaticallt in time.
Psn in the blood stream if it just stays there in the blood and does nothing evil to any organs the blood components itself is often not a problem. It causes problems by attaching to use, organs or whatever, in medicine you use drugs to prevent it from attaching.
The drug should work as long till your body got rid of the psn.
Ofc there are also drugs that do change the psn into different forms.