What is antivenom?

WHAT IS ANTIVENOM?

Antivenoms are purified antibodies against venoms or venom components. Antivenoms are produced from antibodies made by animals to injected venoms.  Antivenom is the only definitive treatment for effective bites by venomous Australian snakes. Prior to the availability of antivenom, death ensued in approximately 45% of tiger snake envenomations  and more than 90% of taipan envenomations. The decision to use antivenom should be based on the patient's history, examination and pathologic findings, and the type of antivenom used will depend on geographic, clinical and pathologic factors.

Most Australian antivenoms are produced using horse-derived antibodies.

The most commonly used animal in the production of Australian antivenoms is the horse. Sheep, rabbits and dogs are also currently used in Australia.

HOW IS ANTIVENOM MADE?

Venom is obtained from the various creatures in different ways.  Snakes and funnel web spiders are milked for their venom.  Stonefish, redback spider and box jellyfish antivenoms are made from venom extracted from the animal by dissection.  This may be a dangerous process.

Small doses of venom or venom components are injected into the animal, and the dose gradually increased as the animal builds up a tolerance to the venom. In response to the introduction of the venom (a foreign substance), the animal produces antibodies to the venom. When the doses being injected are large, the amount of antibody produced is large.

These antibodies are harvested by taking blood from the animals and separating out the antibodies, which are then fragmented and purified by a series of digestion and processing steps.

Horse blood inoculated with tiger and brown snake venoms

When injected into a patient, the binding sites on the antibody fragments bind to the venoms or venom components in the circulation and neutralize the activity of the venoms in the patient. Antivenoms have been made since the 1890s.

Australia was one of the first countries in the world to experiment with snake antivenoms, in 1898, when Frank Tidswell commenced immunization of a former ambulance horse with tiger snake (N. scutatus) venom.

CSL Ltd is the sole manufacturer of antivenoms for human use in Australia. Australian antivenoms are amongst the best in the world, in terms of purity and adverse reaction rate.

Australian Snake Antivenoms	Produced in:	Other Australian Antivenoms	Produced in:
Tiger snake antivenom	Horses	Funnel web spider antivenom	Rabbits
Brown snake antivenom	Horses	Redback spider antivenom	Horses
Taipan antivenom	Horses	Australian paralysis tick antivenom	Dogs
Black snake antivenom	Horses	Box jellyfish antivenom	Sheep
Death adder antivenom	Horses	Stonefish antivenom	Horses
Sea snake antivenom	Horses
Polyvalent snake antivenom	Horses

CHOICE OF ANTIVENOM: SNAKE IDENTIFICATION

Identification of the offending snake will aid in the choice of the appropriate antivenom and alert clinicians to particular features characteristic of envenomation by that type of snake.

In cases of snakebite involving zoo staff, herpetologists or other experienced snake handlers, the snake’s identity may be known (although this cannot always be relied upon, particularly in the case of enthusiastic amateurs).

Identification of snakes by the general public or by hospital staff is frequently unreliable. Sometimes, the snake is not seen, or is only glimpsed in retreat. In these cases, a snakebite venom detection kit may be used.

CSL Snake Venom Detection Kit including contents and packaging.

Australia is the only country in the world that has snake venom detection kits.They consist of a rapid two step enzyme immunoassay in which wells are coated with antibodies to the various snake venoms. A swab from the bite site, blood, or urine helps to select the type of snake antivenom which may have to be used. Note that the primary purpose of the venom detection kit is not to decide whether envenomation has occurred (i.e. whether antivenom is indicated), but to help to choose the appropriate antivenom if required