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Medicine for the Outdoors

Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.

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Antivenom for Neurotoxicity from Scorpion Stings

In the May 14, 2009 issue of the New England Journal of Medicine, in an article entitled “Antivenom for Critically Ill Children with Neurotoxicity from Scorpion Stings,” Dr. Leslie Boyer and colleagues report the results of a study in which the efficacy of scorpion-specific F(ab)’2 antivenom was compared to placebo in the treatment of 15 children ages 6 months to 18 years who were admitted to a pediatric intensive care unit with clinically significant signs of scorpion envenomation (N Engl J Med 2009;360:2090-8). The primary clinical end point was the resolution of the clinical syndrome within 4 hours after administration of the study drug. Secondary end points included the total dose of concomitant midazolam (Versed) – a sedative – and quantitative plasma (bloodstream) venom levels, before and after treatment.

The results showed that the clinical syndrome resolved more rapidly among recipients of the antivenom than among recipients of placebo, with a resolution of symptoms in all 8 antivenom recipients versus one of 7 placebo recipients within 4 hours after treatment. More midazolam was given to the placebo recipients (by necessity to treat symptoms) than in the antivenom recipients. Plasma venom concentrations were undetectable in all 8 antivenom recipients, but in only one placebo recipient one hour after treatment, which indicates that the antivenom neutralized circulating antivenom.

The conclusions are very helpful for clinicians treating scorpion envenomation syndromes with neurotoxic manifestations in critically ill children. They are that intravenous administration of scorpion-specific F(ab)’2 antivenom resolved the clinical syndrome within 4 hours, reduced the need for concomitant sedation with midazolam, and reduced the levels of circulating unbound venom.

This is very important new information. It is estimated that in North America, predominately in Mexico, more than 250,000 people per year are stung by scorpions. The major culprits are of the genus Centruroides. The antivenom used in this study was scorpion-specific F(ab)’2 antivenom (Anascorp, Centruroides [scorpion] immune F(ab)2 intravenous [equine], Instituto Bioclon).

The authors note that there has never been an approved, marketed antivenom therapy for scorpion envenomation in the United States. The only previously available scorpion antivenom in the U.S. was a goat-derived whole IgG (immunoglobulin G) preparation that has not been produced since 1999. Based on the current study, it now appears that there is a relatively safe product for treatment of critically ill children. Its use for critically ill adults and for children and adults with non-critical scorpion envenomation syndromes remains to be studied with the degree of rigor necessary to suggest its regulatory approval for use in the U.S.

image courtesy of Phoenix

Preview the Annual Meeting of the Wilderness Medical Society, which will be held in Snowmass, Colorado July 24-29, 2009.

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Dr. Paul S. Auerbach is the world’s leading authority on wilderness medicine.