There are only a few known antidotes, one of which is a compound derived from milk thistle.

The only known antidote is phylloxera-resistant American vine roots.

There is no known antidote, save one I carry.

There is no known antidote to this poison.

Of course, there were certain snake poisons that had no known antidote.

The effect is irreversible and there is no known antidote.

No known antidote had ever been found.

There is no known antidote, and the victims of such poisonings are often diagnosed as having died from food poisoning.

There's no known antidote, before or after the fact-though we can minimize some of the nastier physical effects.

There was nothing to be done, for this venom has no known antidote.