Antitoxin

An antitoxin was an antibody with the ability to neutralize a specific toxin.

In 2268, Leonard McCoy told James T. Kirk there was no antitoxin for poison of the mugato after Kirk had been bitten by the creature. 

Ryetalyn was the only known antidote for Rigelian fever, and as such an antitoxin could be made from it. However this antitoxin could be rendered inert and useless by irillium. 

In 2269, McCoy administered the antitoxin dylovene to Hikaru Sulu when he was poisoned by a retlaw plant. 

Later that year, McCoy created an antitoxin was from the sur-snake's venom to reverse the surgo-op, a mutation Spock and James T. Kirk had undergone that had transformed them into water-breathers.