An antitoxin is an antibody

Antibody

An antibody, also known as an immunoglobulin, is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects such as bacteria and viruses. The antibody recognizes a unique part of the foreign target, termed an antigen...

 with the ability to neutralize a specific toxin

Toxin

A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...

. Antitoxins are produced by certain animal

Animal

Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...

s, plants, and bacteria. Although they are most effective in neutralizing toxins, they can kill bacteria and other microorganisms. Antitoxins are made within organisms, but can be injected into other organisms, including humans. This procedure involves injecting an animal with a safe amount of a particular toxin. Then, the animal’s body makes the antitoxin needed to neutralize the toxin. Later, the blood

Blood

Blood is a specialized bodily fluid in animals that delivers necessary substances such as nutrients and oxygen to the cells and transports metabolic waste products away from those same cells....

 is withdrawn from the animal. When the antitoxin is obtained from the blood, it is purified and injected into a human or other animal, inducing passive immunity

Passive immunity

Passive immunity is the transfer of active humoral immunity in the form of readymade antibodies, from one individual to another. Passive immunity can occur naturally, when maternal antibodies are transferred to the fetus through the placenta, and can also be induced artificially, when high levels...

. To prevent serum sickness

Serum sickness

Serum sickness in humans is a reaction to proteins in antiserum derived from an non-human animal source. It is a type of hypersensitivity, specifically immune complex hypersensitivity . The term serum sickness–like reaction is occasionally used to refer to similar illnesses that arise from the...

, it is often best to use antitoxin generated from the same species (e.g. use human antitoxin to treat humans).