Anascorp: the bark scorpion antivenom
Anascorp is a purified horse-derived antibody fragment (F(ab')2) that binds Centruroides venom toxins so they can no longer act on nerve sodium channels.[1] The FDA approved it in August 2011 after a University of Arizona-led randomized trial in which children with neurotoxic signs recovered within about four hours on antivenom while placebo patients did not.[2][3] It is reserved for grade III and IV envenomations.[4]
What is Anascorp?
Anascorp (Centruroides immune F(ab')2 equine injection) is made by immunizing horses with Centruroides venom, harvesting the antibodies, and cleaving off the part of the antibody most likely to cause allergic reactions. The remaining F(ab')2 fragments bind circulating venom toxins.[1] It was developed in Mexico, where Centruroides stings are a major public-health problem, and tested in Arizona.[3]
What did the trial show?
The pivotal study, published in the New England Journal of Medicine in 2009, randomized critically ill children with neurotoxic scorpion envenomation to antivenom or placebo. Systemic signs resolved within four hours in the antivenom group and persisted in the placebo group; antivenom patients needed far less midazolam sedation and had lower venom levels in their blood at one hour.[2] The FDA approved Anascorp on the strength of that trial in 2011, the first scorpion antivenom approved in the United States.[3]
Who receives it?
Patients with grade III or IV envenomation: cranial-nerve signs (roving eyes, drooling, trouble swallowing) and/or neuromuscular jerking.[4] In practice that is mostly young children, because they have the highest rates of severe reaction.[6] Grade I and II stings, the great majority, are managed with pain control and observation.[4] Emergency departments across Arizona stock it.
What are the side effects?
Like any animal-derived antibody product, it can cause allergic reactions, including rare anaphylaxis, and delayed serum sickness (fever, rash, joint pain) days to weeks later.[1] The trial and post-marketing experience found these uncommon. Clinicians weigh those risks against the alternative, which before 2011 was days of intensive sedation and airway monitoring.[2]
What was done before antivenom?
Supportive care: benzodiazepines for agitation and jerking, opioids for pain, and sometimes intubation for airway protection, over one to two days.[4] Arizona Poison Control had used an earlier goat-derived antivenom produced at Arizona State University for decades, but it was never FDA-approved and production ended in the late 1990s.[3]
Devon "The Scorpion Guy" at ArizonaBarkScorpion.org. "Anascorp: How the Bark Scorpion Antivenom Works." 2026-09-12. https://arizonabarkscorpion.org/antivenom/Related
Sources for this page
- Anascorp (Centruroides immune F(ab')2 equine injection): prescribing information and sting guidance. Rare Disease Therapeutics. www.anascorp-us.com/Tier 1
- Boyer LV, Theodorou AA, Berg RA, et al. Antivenom for Critically Ill Children with Neurotoxicity from Scorpion Stings. New England Journal of Medicine 360(20):2090-2098, 2009. www.nejm.org/doi/full/10.1056/NEJMoa0808455Tier 1
- Flinn Foundation. FDA grants approval to scorpion antivenom tested by UA team, 2011. www.flinn.org/fda-grants-approval-to-scorpion-antivenom-tested-by-ua-team/Tier 2
- Grigsby A, DO. Bark Scorpion Stings. American Academy of Emergency Medicine Resident and Student Association, 2017. www.aaemrsa.org/bark-scorpion-stings/Tier 2
- Ruha A-M, MD. What You Need to Know About Scorpion Stings. University of Arizona Health Sciences, June 12, 2023. healthsciences.arizona.edu/news/blog/what-you-need-know-about-scorpion-stingsTier 2
- Kang AM, Brooks DE. Nationwide Scorpion Exposures Reported to US Poison Control Centers from 2005 to 2015. Journal of Medical Toxicology 13(2), 2017. link.springer.com/article/10.1007/s13181-016-0594-0Tier 1