Antitoxin

Antitoxin is a vial of medicine that nullifies poison damage caused by cyanide-tipped rounds and poisoned crossbow bolts. The item appears in The Operative: No One Lives Forever missions The Dive and Such Is the Nature of Revenge.

While Cate Archer was exploring the sunken Freighter Lorelei she found a vial of Antitoxin within the ship's galley.

When the lasers are tripped in the Safecracker vault, the poison released is made useless if the Antitoxin is equipped, allowing free roaming of the now inescapable vault.

When Archer was confronted by Melvin Blitzny in the English church graveyard, there was a vial of Antitoxin available on the grounds.

External link
Antitoxin on Wikipedia