* Anti- (Greek: ἀντί) means "against," "opposite," or "in opposition to."
* Tox- (Greek: τόξον) means "poison," "bow," or "arrow" (related to the idea of poisoned arrows).
Considering these roots, the word that most likely means a method working against effects of a poisonous substance is antitoxin.
Antitoxin refers to a substance that counteracts the effects of a toxin.