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Recently, out of curiosity, I looked online if snake antivenom for humans were actually sold for individuals. I found out they aren't. Not only that, but bills can get really high on countries that don't provide them in public healthcare (i.e.: USA), as in 4 digit numbers. Makes one disappointed to realize the price of production of human-use antivenom is actually really small in comparison to what they are charged for[1]:

Antivenom Price

On the other side, veterinary antivenom is sold for treating animals attacked by some venomous snake. The brand I found for sale[2] is a polyvalent antivenom: A solution of specific equine immunoglobulins, purified by enzymatic digestion and lyophilizated (freeze-dried), obtained from hyperimmunized Equidae with Crotalus ("Cascavel" aka Rattlesnake), Bothrops ("Jararaca") and Lachesis ("Surucucu" aka Bushmasters) snake venom. I included the common-names in Portuguese since these are the 3 common vipers found in Brazil, where this particular antivenom is sold. Coral snakes (Elapidae) are also found here, but I didn't find any veterinary antivenom for those (and this one I found isn't recommended for bites from them).

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Some veterinary-use antivenom shows more side-effects on animals than others, specially unpurified Equine Plasma antivenom, which can cause allergic skin reactions near the application site and peripheral lymphadenopathy 48h after application[3]. The same source comments on other types of veterinary antivenom, but I'm not sure which the one I found classify on (if any, because of the targeting snakes being slightly different). The description of F(ab’)2 antivenom resembles the one provided by the brand I found: Both are purified, enzymatically cleaved/digested, lyophilized and obtained from horses.

Technically, what is the difference between the antivenom for human usage and veterinary antivenom? In an hypothetical situation that one gets bitten far from medical help, how big would be the risk of applying a veterinary antivenom? Obviously injecting drugs that are not FDA approved is not recommended, and considering the number of snake-bite related deaths is relatively low in some continents[4] it would be unwise to even give people the idea of using unapproved drugs to treat bites. I was just wondering if, after assessing a situation and realizing medical help won't come (or come in time), having one of those in hand could save a person's life after a viper bite.


UPDATES:

There's a scientific article published in the British Journal of Clinical Pharmacology, entitled "Adverse reactions to snake antivenom, and their prevention and treatment"[5], that brings light to the adverse reactions to snake antivenom. Severe systemic anaphylaxis rates can be as high as 40%, specially in places where the antivenom manufacture quality is dubious. Antihistamines and hydrocortisone didn't prove effective in controlling the antivenom acute reactions, and only adrenaline seemed like a decent prophylatic treatment to anaphylaxis. The management of antivenom acute reactions is as big of an issue as the treatment of the envenoming itself. And I'm still talking about antivenom approved for human-usage.

Speculation: Polyvalent antivenom could be more problematic than specific antivenom, because more unnecessary foreign proteins must be injected to treat the same amount of venom. Not only that, but probably the companies that manufacture veterinary antivenom are not as worried about their quality (and purification process) as ones that are more tightly regulated to produce human antivenom. For that reason, acute anaphylaxis would be more likely while using those.

Whether the risk of anaphylatic reaction is compensated by the risk of untreated envenoming is still not clear (one might say it's a question that won't have a definitive answer, or even opinion-based). I'll keep adding any new information that brings more light to the issue, but answers from people more knowledgeable in the area are very welcome!

References:

[1]: https://www.washingtonpost.com/news/wonk/wp/2015/09/09/the-crazy-reason-it-costs-14000-to-treat-a-snakebite-with-14-medicine/?noredirect=on&utm_term=.b4855c4e100c

[2]: https://www.dechra.com.br/produto-detalhe/102/master-soro-plus

[3]: https://vetgirlontherun.com/veterinary-continuing-education-update-antivenom-treatments-animals-raegan-wells-vetgirl-blog/

[4]: https://animals.mom.me/snake-bite-death-statistics-worldwide-2431.html

[5]: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4767202/pdf/BCP-81-446.pdf

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You inject a horse with the venom and in return you get in its blood anti-venom antibodies. Those antibodies will be poorly tolerated in humans and shall produce an allergic reaction, even more if the individual already received horse antibodies in the past (that's how anti-(goat-IgG) antibodies are made). They will be also less efficient due to differences in the constant region of the horse antibodies, not binding well to the human Fc receptor.

One solution is to cleave the horse IgG with pepsin or papain protease to separate the F(ab’)2 or Fab fragments. But still it won't bind to Fc receptors and the renal clearance will be also faster. The good point is that such antivenom can be administered more safely to any species.

For human use the best solution is to use sequencing, plasmids, in-vitro culture, to make recombinant antibodies merging the human constant region with the variable region of horse anti-venom IgG but that's a more expensive biotechnology. And the obtained recombinant IgG will pose the same allergy problem as the whole horse IgG in other species.

It is shamely common for drugs that the manufacturers don't give enough information to tell what is what. It may very well happen that the FDA approved expensive vials are old whole IgG and that a much cheaper internet veterinary antivenom is using the recent technologies.

https://vetgirlontherun.com/veterinary-continuing-education-update-antivenom-treatments-animals-raegan-wells-vetgirl-blog/

https://www.mdpi.com/2072-6651/14/9/606/pdf

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