Snake antivenom

Antivenoms are typically produced using a donor animal, such as a horse or sheep. The donor animal is hyperimmunized with non-lethal doses of one or more venoms to produce a neutralizing antibody response. Then, at certain intervals, the blood from the donor animal is collected and neutralizing antibodies are purified from the blood to produce an antivenom.{{cite book | author=WHO Expert Committee on Biological Standardization | year=2017 | location=Geneva, Switzerland | title=WHO Expert Committee on Biological Standardization, sixty-seventh report | publisher=World Health Organization (WHO) | hdl=10665/255657 | id=WHO technical report series;1004. License: CC BY-NC-SA 3.0 IGO | isbn=978-92-4-069645-7 | issn=0512-3054 | hdl-access=free | pages=197–388 | chapter=Annex 5; Guidelines for the production, control and regulation of snake antivenom immunoglobulins;Replacement of Annex 2 of WHO Technical Report Series, No. 964 | chapter-url=https://www.who.int/bloodproducts/AntivenomGLrevWHO_TRS_1004_web_Annex_5.pdf | access-date=20 January 2020 | archive-date=14 February 2020 | archive-url=https://web.archive.org/web/20200214211543/https://www.who.int/bloodproducts/AntivenomGLrevWHO_TRS_1004_web_Annex_5.pdf | url-status=live }}

• Human Medicine: In the United States, antivenom production and distribution is regulated by the Food and Drug Administration.
• Veterinary Medicine: In the United States, antivenom production and distribution is regulated by the United States Department of Agriculture's Center for Veterinary Biologics.

Snake antivenom can be classified by which antigens (venoms) were used in the production process. If the hyperimmunizing venom is obtained from a single species, then it is considered a monovalent antivenom. If the antivenom contains neutralizing antibodies raised against two or more species of snakes, then the composition is considered polyvalent.

Compositions of the antivenom can be classified as whole immunoglobulin G (IgG), or fragments of IgG. Whole antibody products consist of the entire antibody molecule, often IgG, whereas antibody fragments are derived by digesting the whole IgG into Fab (monomeric binding) or F(ab')2 (dimeric binding). The fragment antigen-binding region, or Fab, is the selective antigen-binding region. An antibody, such as IgG, can be digested by papain to produce three fragments: two Fab fragments and one Fc fragment. An antibody can also be digested by pepsin to produce two fragments: a F(ab')₂ fragment and a pFc' fragment.

The fragment antigen-binding (Fab fragment) is a region on an antibody that binds to antigens, such as venoms. The molecular size of Fab is approximately 50kDa, making it smaller than F(ab')₂ which is approximately 110kDa. These size differences greatly affect the tissue distribution and rates of elimination.

Antivenoms may also have some cross protection against a variety of venoms from snakes within the same family or genera. For instance, Antivipmyn (Instituto Bioclon) is made from the venoms of Crotalus durissus and Bothrops asper. Antivipmyn has been shown to cross neutralize the venoms from all North American pit vipers.{{cite journal | vauthors = Sánchez EE, Galán JA, Perez JC, Rodríguez-Acosta A, Chase PB, Pérez JC | title = The efficacy of two antivenoms against the venom of North American snakes | journal = Toxicon | volume = 41 | issue = 3 | pages = 357–65 | date = March 2003 | pmid = 12565759 | doi = 10.1016/s0041-0101(02)00330-6 }} Cross neutralization affords antivenom manufacturers the ability to hyperimmunize with fewer venom types to produce geographically suitable antivenoms.

Snake antivenom is complicated for manufacturers to produce.{{cite news|last1=Lewis|first1=Danny|title=Why A Single Vial Of Antivenom Can Cost $14,000|url=http://www.smithsonianmag.com/smart-news/why-single-vial-antivenom-can-cost-14000-180956564/|access-date=9 January 2017|work=Smithsonian|date=11 September 2015|archive-date=3 May 2019|archive-url=https://web.archive.org/web/20190503011426/https://www.smithsonianmag.com/smart-news/why-single-vial-antivenom-can-cost-14000-180956564/|url-status=live}} When weighed against profitability (especially for sale in poorer regions), the result is that many snake antivenoms, world-wide, are very expensive. Availability, from region to region, also varies.{{cite web|url=https://www.pharmaceutical-technology.com/features/antivenom-supply-snake-bites/|website=www.pharmaceutical-technology.com|title=Antivenom Supply for Snake bites|date=24 April 2019|access-date=25 July 2020|archive-date=10 January 2021|archive-url=https://web.archive.org/web/20210110030309/https://www.pharmaceutical-technology.com/features/antivenom-supply-snake-bites/|url-status=live}}

{{as of|2012}}, the relative rarity of coral snake bites, combined with the high costs of producing and maintaining an antivenom supply, means that antivenom (also called "antivenin") production in the United States has ceased. According to Pfizer, the owner of the company that used to make the antivenom Coralmyn, it would take $5–$10 million for researching a new synthetic antivenom.{{citation needed|date=October 2012}}{{clarify|date=October 2012}} The cost was too high in comparison to the small number of cases presented each year. The existing American coral snake antivenom stock technically expired in 2008, but the U.S. Food and Drug Administration has extended the expiration date every year through to at least 30 April 2017.{{needs update inline|date=September 2024}}{{cite web | url=https://www.fda.gov/BiologicsBloodVaccines/SafetyAvailability/ucm445083.htm | title=Safety & Availability (Biologics) > Expiration Date Extension for North American Coral Snake Antivenin (Micrurus fulvius) (Equine Origin) Lot 4030026 Through October 31, 2014 | publisher=Food and Drug Administration | access-date=19 March 2016 | archive-date=3 March 2016 | archive-url=https://web.archive.org/web/20160303142551/http://www.fda.gov/biologicsbloodvaccines/safetyavailability/ucm445083.htm | url-status=live }}{{cite news | last = Breen | first = David | newspaper = Orlando Sentinel | date = 12 October 2013 | title = Risk from coral-snake bites grows as antivenin dwindles | url = https://www.orlandosentinel.com/2013/10/12/risk-from-coral-snake-bites-grows-as-antivenin-dwindles/ | access-date = 25 May 2014 | archive-date = 24 May 2014 | archive-url = https://web.archive.org/web/20140524064724/http://articles.orlandosentinel.com/2013-10-12/news/os-coral-snakebite-treatment-shortage-20131008_1_coral-snake-bites-antivenin-fda | url-status = live }}

Foreign pharmaceutical manufacturers have produced other coral snake antivenoms, but the costs of licensing them in the United States have stalled availability.{{cite web |url=http://www.popularmechanics.com/science/health/snakebites-about-to-get-more-deadly |title=Antivenom Shortages – Cost of Antivenom Production Creates Shortages |publisher=Popular Mechanics |date=10 May 2010 |access-date=16 November 2010 |archive-date=13 May 2010 |archive-url=https://web.archive.org/web/20100513022759/http://www.popularmechanics.com/science/health/snakebites-about-to-get-more-deadly |url-status=live }} Instituto Bioclon is developing a coral snake antivenom.{{cite web |url=http://www.bioclon.com.mx/bioclon/html/coralmyn_en.html |title=Our Products – Coralmyn |publisher=Bioclon.com.mx |access-date=16 November 2010 |archive-url=https://web.archive.org/web/20101013102552/http://www.bioclon.com.mx/bioclon/html/coralmyn_en.html |archive-date=13 October 2010 |url-status=dead }} In 2013, Pfizer was reportedly working on a new batch of antivenom but had not announced when it would become available. {{As of|2016}}, the Venom Immunochemistry, Pharmacology and Emergency Response (VIPER) institute of the University of Arizona College of Medicine was enrolling participants in a clinical trial of INA2013, a "novel antivenom," according to the Florida Poison Information Center.{{cite web | url=http://www.poisoncentertampa.org/poison-topics/coral-snake-antivenom/ | title=Coral Snake Antivenom - Poison Center Tampa | publisher=Poison Center Tampa | access-date=19 March 2016 | archive-date=1 April 2016 | archive-url=https://web.archive.org/web/20160401044750/http://www.poisoncentertampa.org/poison-topics/coral-snake-antivenom/ | url-status=live }}{{cite web | url=https://clinicaltrials.gov/ct2/show/NCT01337245?term=coral+snake&rank=1 | title=Emergency Treatment of Coral Snake Envenomation With Antivenom - Full Text View - ClinicalTrials.gov | publisher=National Institutes of Health | access-date=19 March 2016 | archive-date=30 March 2016 | archive-url=https://web.archive.org/web/20160330094712/https://clinicaltrials.gov/ct2/show/NCT01337245?term=coral+snake&rank=1 | url-status=live }}

Over 600 species are known to be venomous—about a quarter of all snake species. The following table lists some major species.

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• {{cite book | vauthors=((Regional Office for South-East Asia)), ((World Health Organization)) | year=2016 | title=Guidelines for the management of snakebites | edition=2nd | publisher=World Health Organization | hdl=10665/249547 | isbn=978-92-9022-530-0 | hdl-access=free }}
• {{cite book | vauthors=((World Health Organization)) | year=2019 | title=Snakebite envenoming: a strategy for prevention and control | publisher=World Health Organization | hdl=10665/324838 | id=License: CC BY-NC-SA 3.0 IGO | isbn=978-92-4-151564-1 | hdl-access=free }}

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Category:Antitoxins

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