Antivenoms


Antivenoms are prepared from immunized animal sera. They constitute the specific treatment for snake, spider and scorpion envenomation.
 
Incidence
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%.
 
Mechanisms
IgE-mediated hypersensitivity.
 
Circulating immune complexes (serum sickness).
 
Complement activation by antivenom or impurities.
 
Management
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.

References

  1. Ismail M, "The treatment of the scorpion envenoming syndrome: the Saudi experience with serotherapy", Toxicon. 1994; 32 (9): 1019-26
  2. Gateau T, Bloom M, Clark R, "Response to specific centuroides sculpturatus antivenom in 151 cases of scorpion stings", J. Clin. Toxicol. 1994; 32 (2): 165-71
  3. Varma T, "Rapid desensitization in antivenom hypersensitivity", J. Assoc. Phys. Ind. 1987; 35 (3): 250-1
  4. Malasit P, Warrell DA, Chanthavanich P,Viravan C, Mongkolsapaya J, Singhthong P, Supich C, "Prediction, prevention and mechanisms of early (anaphylactic) antivenom reactions in victims of snake bites", Br. Med. J., 1986 . 292: 17–20.
  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.