What is the management and pharmacology for pit viper and coral snake envenomation in the United States, as per the United States Medical Licensing Examination (USMLE)?

From the Guidelines

Management of pit viper and coral snake envenomation should prioritize administering specific antivenom as soon as possible, with CroFab for pit vipers and North American Coral Snake Antivenom for coral snakes, while avoiding outdated techniques like tourniquets, incision and suction, or cryotherapy. The treatment approach differs significantly due to the distinct venom mechanisms of these snakes. For pit vipers (rattlesnakes, copperheads, cottonmouths), treatment involves administering CroFab (crotalidae polyvalent immune Fab) antivenom as soon as possible after assessing severity through progressive swelling, ecchymosis, and systemic symptoms, as recommended by the latest guidelines 1. The initial dose is typically 4-6 vials given intravenously, with additional doses based on clinical response. Supportive care includes wound care, tetanus prophylaxis, pain management, and monitoring for coagulopathy.

For coral snake envenomation, which causes neurotoxic symptoms, North American Coral Snake Antivenom is the specific treatment, administered as 3-5 vials initially with potential additional doses. Airway management is critical as respiratory paralysis may occur. Laboratory monitoring should include complete blood count, coagulation studies, and metabolic panel for both types of envenomation. Field management includes immobilizing the affected limb, removing constrictive items, and rapid transport to medical care, as outlined in the 2024 American Heart Association and American Red Cross guidelines for first aid 1. It is also reasonable to rest and immobilize the bitten extremity and minimize exertion by the person who was bitten if it does not delay access to emergency medical care 1.

Key points to consider in management include:

• Activating emergency services for any person bitten by a venomous or possibly venomous snake 1
• Removing rings and other constricting objects from the bitten extremity 1
• Avoiding the application of ice to a snakebite wound, as it is of unproven benefit and may be harmful in some situations 1
• Not using suction, electric shock, tourniquets, or pressure immobilization bandaging to treat snake bites, as these methods are potentially harmful 1

From the FDA Drug Label

CROFAB is a sheep-derived antivenin indicated for the management of adult and pediatric patients with North American crotalid envenomation For intravenous use only Initiate administration as soon as possible after snake bite in patients who develop signs of envenomation Dose: Recommended initial dose is between 4 and 6 vials Observe patient for up to one hour after the initial dose and give an additional 4-6 vial dose as needed to gain initial control of envenomation After initial control is established, administer additional 2-vial doses every 6 hours for 18 hours (total of 3 doses)

The management and pharmacotherapy for pit vipers and coral snakes involves the use of CROFAB (Crotalidae Polyvalent Immune Fab), a sheep-derived antivenin. The recommended initial dose is 4-6 vials, administered intravenously as soon as possible after the snake bite, with additional doses given as needed to gain initial control of envenomation.

• Key points:
  • Initiate administration as soon as possible after snake bite
  • Recommended initial dose: 4-6 vials
  • Observe patient for up to one hour after the initial dose and give an additional dose as needed
  • Administer additional 2-vial doses every 6 hours for 18 hours (total of 3 doses) after initial control is established
  • Monitor patients for recurrent coagulopathy for one week or longer following treatment of the bite 2
  • Hypersensitivity reactions, including anaphylaxis, may occur 2
  • Patients allergic to papain, chymopapain, papaya extracts, or bromelain (pineapple enzyme), may react to CROFAB 2

From the Research

Management of Pit Vipers and Coral Snakes

• The mainstay of hospital treatment for venomous snakebite is antivenom 3.
• There is currently only one antivenom available in the United States for the treatment of pit viper envenomation, Antivenin (Crotalidae) Polyvalent (ACP) 3.
• The general indication for the administration of antivenom is presence of progressive venom injury, defined as worsening local injury, a clinically important coagulation abnormality, or systemic effects 3.

Pharmacology

• A new antivenom, CroFab (FabAV), composed of purified Fab specific to indigenous snake species, has been demonstrated to be effective in prospective trials 3.
• FabAV appears to be as effective as IgG antivenoms, but has a shorter half-life and may allow recurrence of venom effects if additional doses are not administered 3.
• The Fab preparation has produced fewer acute or delayed (serum sickness) allergic reactions, but further experience is needed to confirm this observation 3.

Treatment of Pit Viper Envenomation

• Coagulation abnormalities following crotaline (pit viper) snakebite can be recurrent or persistent, and may occur as late as 2 weeks following envenomation 4.
• Patients treated with Fab-based antivenom may benefit from periodic rather than single-bolus dosing 4.
• Crotaline Fab antivenom appears to be effective in cases of severe North American pit viper envenomation, with 77% of severe venom effects improving or resolving after FabAV therapy 5.

Emergency Department Management

• Treatment of North American snake envenomations relies on supportive care, plus antivenom for select cases 6, 7.
• Controversies exist with regard to prehospital use of pressure immobilization, antivenom use, coagulation testing after copperhead envenomation, and fasciotomy 6, 7.