Antivenoms are prepared from immunized animal sera. They constitute the specific treatment for snake, spider and scorpion envenomation.
Snake: 3 to 54%.
Spider: 0.5% .
Scorpion: 8% with centuroides sculpturatus antivenom.
1.7 to 2.6% with L. quinquestriatus venom.
Risk factors
Allergy to animal serum or dander (horse, goat).
Clinical manifestations
Immediate: anaphylactic shock, urticaria, pruritus, rash, bronchospasm, vomiting, abdominal pain, diarrhea.
Delayed: serum sickness, arthralgias, urticaria, polyadenopathy .
Diagnostic methods
Cutaneous testing: its usefulness is controversial. False positive and negative seem to be high.
Nevertheless, with centuroides sculpturatus antivenom specificity is 98%, sensitivity 68%.
IgE-mediated hypersensitivity.
Circulating immune complexes (serum sickness).
Complement activation by antivenom or impurities.
In high risk patients, perform intradermal skin tests.
  • If positive, the risk of immediate reaction is high
  • Negative results do not absolutely rule out the possibility of a reaction.

Pre-treatment with antihistamine and epinephrine, and slow intravenous injection of the antivenom at a 1/1000 or 1/10000 dilution are good precautions.

Rapid desensitization has been recommended.


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  5. Otten EJ, Mackimm D, "Venomous snakebite in a patient allergic to horse serum", Ann. Emerg. Med., 1983; 12: 624–7.
  6. Sutherland SK, Lovering KE, "Antivenoms", Med. J. Austr., 1979; 671–4.

As in all diagnostic testing, the diagnosis is made by the physican based on both test results and the patient history.