Antifreeze contains ethylene glycol or methanol both of which are poisonous. It is also sweet in taste which causes some pet deaths. It only takes 1 teaspoon to kill a 7lb cat. In small doses it can reproduce the effects of alcohol, but the poisons in it make it fatal if you drink even 100mL. Even before you get to the fatal dose you will probably go blind and experience kidney failure so its a terrible substitute for alcohol fyi.
The poison can be somewhat counteracted by drinking whiskey shortly after. It can also be counteracted with fomepizole. Induced vomiting is recommended as well.
If your pet happens to drink some antifreeze feed it soft food and/or milk then induce vomiting with syrup of ipecac. Whiskey and fomepizole may also work.
Medical treatment is going to be necessary as well.
Hope you never have to use this info.