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INTRODUCTION

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The terms “antivenom” and “antivenin” often are used interchangeably. Although the origin of the term “antivenom” is obvious, “venin” is French for venom and “antivenin” is traditionally used in certain parts of the world. Wyeth Pharmaceuticals, the maker of Crotaline and Micrurus antivenom, and Merck & Co., Inc., the maker of Latrodectus antivenom, adopted “antivenin” in the brand names for their products. Brand name recognition has largely been responsible for the use of the term “antivenin” in place of “antivenom”. In 1981, the World Health Organization determined the preferred terms for the English language to be “venom” and “antivenom.”

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HISTORY

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Of the species of spiders of medical importance in the United States, two of the most notable are Latrodectus (L. mactans, L. geometricus, L. vaiolus, L. hesperus, and L. bihopi are native, while L. geometricus was introduced) and Loxosceles. Although commercially available antivenom exists in the United States for treatment of Loxosceles envenomation, antivenom produced for South American Loxosceles spiders demonstrates cross-reactivity with North American species like L. reclusa.12 Currently, one commercially available Latrodectus antivenom exists in the United States. Black widow spider antivenin (Merck & Co., Inc.) (Merck BW-AV) has been available in the United States since its U.S. Food and Drug Administration (FDA) approval in 1936.3 The use of this antivenom in the treatment of Latrodectus envenomations remains controversial, as mortality from these bites is low in the United States,7,8,30,32 and complications including death following antivenom administration are rarely reported.7,20,31 Most recently, severe production shortages have necessitated emergency release of the product by the manufacturer within 24 hours of notification of a patient with symptoms from a presumed envenomation.1 Ongoing research and development of an F(ab′)2 antivenom may ameliorate concerns and limitations related to potential adverse events resulting from administration of the Merck antivenom and production shortages limiting availability.11

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PHARMACOLOGY

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Chemistry, Preparation, and Mechanism of Action

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Antivenom for spiders is prepared in a similar manner as other antivenom products by first immunizing animals with non-toxic amounts of venom.5,25 Monkeys, horses, goats, sheep, chicken, camels, and rabbits have been used historically to source antivenom.28 The animals are placed on an inoculation schedule to allow gradual production of immunoglobulins, most importantly IgG. Sufficient antibody production usually requires up to 6 weeks. Animal choice for immune serum production is more often dictated by the species availability, financial considerations, and tradition rather than scientific modeling. Horses are used by the majority of antivenom producers, since they are relatively easy to maintain, and large volumes of serum can be obtained at one time without harm. Varying efforts are made during antivenom production to remove animal proteins such as albumin. Antivenoms target, bind, neutralize, and promote elimination or redistribution of toxins from body tissues. ...

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