• More than 3,000 species of snakes are identified worldwide, with nearly 800 species considered venomous.
  • All venomous species are classified taxonomically into one of 4 general groups.
  • These include the families Viperidae, Elapidae, and Colubridae, as well as the Atractaspidinae, a subfamily of the Lamprophiidae family.
  • The United States is home to nearly 30 species and subspecies of venomous snakes, with many more found throughout Mexico. All belong to either the Crotalinae subfamily of Viperidae or the Elapidae family.
  • Of crotalid bites for which the type of snake is reported, about half are rattlesnake species, and the remainder copperheads and cottonmouths.
  •  Rattlesnakes are found throughout most of the United States, but encounters are most common in western and southern states.

Rosen’s EM Textbook

Pathophysiology of Snake Venom

  • Specific venom components are expected to be present to various degrees among all North American pit vipers.
  • Pit viper snake venom is a complex pool of more than 100 components that contribute to toxicity
  • Some examples include snake venom metalloproteinases, snake venom serine proteases, phospholipase A2, disintegrins, bradykinin potentiating peptides, C-type lectinlike peptide, and vascular endothelial growth factors.
  • The content, potency, and quantity of these components are dictated by a variety of factors that include but are not limited to the following: genus, species, age, diet, climate (season), and geography.
  • Available human and animal data suggest that venom antigens are absorbed into blood within minutes of envenomation, with peak concentrations detected within 4 hours

Clinical Features

Goldfrank’s Toxicologic Emergencies, 11e

Diagnostic Testing

  • Diagnosis of North American snake envenomation is based on a history of a snakebite and presence of clinical signs of envenomation
  • Platelet counts, fibrinogen concentrations, and PTs are useful in the diagnosis of pit viper envenomation if they are abnormal.
  • However, normal results do not exclude envenomation because thrombocytopenia and coagulopathy do not develop in all patients with pit viper envenomation.


Rosen’s EM Textbook
Rosen’s EM

Craig’s Article on Snake Bite Management

CroFab Website

Anavip Website

Craig Blog Resources
Study tips for ABAT

Related FOAM Posts

Tox and



Ruha A, Pizon AF. Native (US) Venomous Snakes and Lizards. In: Nelson LS, Howland M, Lewin NA, Smith SW, Goldfrank LR, Hoffman RS. eds. Goldfrank’s Toxicologic Emergencies, 11e New York, NY: McGraw-Hill; Accessed January 12, 2020.

Otten EJ. Venomous Animal Injuries. In: Marx, J. A., & Rosen, P. (2014). Rosen’s emergency medicine: Concepts and clinical practice (8th ed.). Philadelphia, PA: Elsevier/Saunders. Accessed January 12, 2020.

Cocchio C, Johnson J, Clifton S. Review of North American pit viper antivenoms. Am J Health Syst Pharm. 2020 Jan 24;77(3):175-187. 

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