Antivenom
A guide to antivenom & alpha-gal syndrome (AGS)
Alpha-gal syndrome
and antivenom
Responding to
venomous snake bites
Select publications
on AGS and antivenom
Alpha-gal syndrome and antivenom
Anti-venom: Alpha-gal is present in anti-venom formulations because these purified fragments are derived from venom-immunized non-primate mammals. There has been at least one case report of an acute reaction to CroFab in a patient with AGS. Despite this report, we advise administration of CroFab if clinically indicated even in patients with AGS as the risk of reaction to anti-venom has not been established in this scenario and may be quite low while, on the contrary, the therapeutic benefit of anti-venom is high.
Both the presence of alpha-gal in some snake antivenom, such as crotalidae polyvalent immune Fab (CroFab) (6,50,51,57), and its association with severe reactions in patients with alpha-gal syndrome has been established (6,50,51,57).
If an envenomation requires antivenom, National Snakebite Support recommends that you treat with antivenom, even if you have alpha-gal syndrome.
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Responding to venomous snake bites
If an envenomation requires antivenom, you treat with antivenom. There is no absolute contraindication.
All antivenoms have alpha-gal to some extent. We have two options when treating an AGS patient with antivenom. We can monitor really carefully and treat if/when signs and symptoms develop, or we can pre-medicate with antihistamines +/- steroids with epinephrine available. You never want to withhold antivenom when it is really necessary. We can treat an allergic reaction.
In the event of a venomous snake bite, contact the National Snakebite Support. National Snakebite Support™ (NSS) connects snakebite victims and healthcare providers with experts who practice and promote evidence-based snakebite management. NSS is familiar with management of snake bites in patients with AGS.
Select publications
on AGS and antivenom
- Banner W, Edelen K, Epperson LC, Moore E. Hypersensitivity reactions due to North American pit viper antivenom administration and confirmed elevation of alpha-gal IgE. Toxicology Communications. 2024;8(1):2314314.
- Wai M, Filip AB, Abbott A, Martin A, Donnell R, Sutton J. Anaphylaxis in Alpha-Gal patients treated with F(ab’) 2 for snake bite venom. Toxicol Commun. 2024;8(1). doi:10.1080/24734306.2024.2392459
- Blessmann J, Hanlodsomphou S, Santisouk B, et al. Serum IgE against galactose-alpha-1,3-galactose is common in Laotian patients with snakebite envenoming but not the major trigger for early anaphylactic reactions to antivenom. Toxicon X. 2020;7:100054.
- Straesser M, Keshavarz B, Borish L, et al. α-Gal on Crotalidae-polyvalent Fab antivenom (CroFab): Investigating the relevance to immediate hypersensitivity reactions. J Allergy Clin Immunol Pract. 2021;9(2):1015-1017.e1.
- Rizer J, Brill K, Charlton N, King J. Acute hypersensitivity reaction to Crotalidae polyvalent immune Fab (CroFab) as initial presentation of galactose-alpha-1,3-galactose (alpha-gal) allergy. Clin Toxicol (Phila). 2017;55(7):668–9.
- Fischer J, Eberlein B, Hilger C, Eyer F, Eyerich S, Ollert M, et al. Alpha-gal is a possible target of IgE-mediated reactivity to antivenom. Allergy. 2017;72(5):764–71.