noun

• (medicine) A medicine able to neutralize a toxin.
  "Through the needle-hole thus stained with dye it was possible to "superinject" antitoxin, using a slightly wider needle avoid back leak along the old needle track, and thus to ensure a distribution of both toxin and antitoxin solutions from the same point the skin."
• (medicine) An antibody capable of neutralizing specific toxins.
  "These albuminous substances, whether found as normal products or created artificially in the blood, are distinguished as antitoxins, protective proteïds, vaccines, or alexines; physiologically they have been divided into sozines, those found in animals naturally immune, and phylaxines, those found in animals which by subcutaneous injections have artificially been made immune."