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Snake Envenomation Overview: Treatment & Medication

Author: Brian James Daley, MD, MBA, FACS, Associate Program Director, Professor, Department of Surgery, Division of Trauma and Critical Care, University of Tennessee School of Medicine
Contributor Information and Disclosures

Updated: Aug 20, 2009

Treatment

Medical Care

Treatment is based on the severity of envenomation; it is divided into field care and hospital management.

Prehospital Care

• As with all medical emergencies, the goal is to support the patient until arrival at the emergency department. The dictum " primum no nocere " (first, do no harm) has significant meaning here because many poorly substantiated treatments may cause more harm than good, including making an incision over the bite, mouth suctioning, tourniquet use, ice packs, or electric shock.
• Appropriate field care should adhere to the basic tenants of emergency life support.
• Reassure the patient during the implementation of ABCs.
• Monitor vital signs and establish at least one large-bore IV and initiate crystalloid infusion. Administer oxygen therapy. Keep a close watch on the airway at all times in case intubation becomes necessary.
• Restrict activity and immobilize the affected area (commonly an extremity); keep walking to a minimum.
• Negative-pressure suctioning devices offer some benefit if used within several minutes of envenomation. Again, do not make an incision in the field.
• Immediately transfer to definitive care.
• Do not give antivenin in the field.

Emergency Department Care

• Physicians who have little experience treating snakebites frequently care for such patients.
• Regional centers often have more experience in the care of snakebite victims. Surgical evaluation for an envenomation victim is paramount.
• Definitive treatment includes reviewing the ABCs and evaluating the patient for signs of shock (eg, tachypnea, tachycardia, dry pale skin, mental status changes, hypotension).
• Evenomation grading determines the need for antivenin in victims of pit viper envenomations. Grades are defined as mild, moderate, or severe.
  • Mild envenomation is characterized by local pain, edema, no signs of systemic toxicity, and normal laboratory values.
  • Moderate envenomation is characterized by severe local pain; edema larger than 12 inches surrounding the wound; and systemic toxicity including nausea, vomiting, and alterations in laboratory values (eg, decreased hematocrit or platelet count).
  • Severe envenomation is characterized by generalized petechiae, ecchymosis, blood-tinged sputum, hypotension, hypoperfusion, renal dysfunction, changes in prothrombin time and activated partial thromboplastin time, and other abnormal test results defining consumptive coagulopathy.

• Grading envenomations is a dynamic process. Over several hours, an initially mild syndrome may progress to a moderate or even severe reaction.
• Horse-serum antivenin has been available since 1956; a purer antivenin with improved properties was released in 2000 (see Medication). With the reduced side-effect profile of antigen-binding fragment antivenom (FabAV) and the improvement in tissue injury with antivenin administration, the threshold for dosing is lower. One study from the southwest United States demonstrated a reduction in rate of fasciotomy after more liberal FabAV dosing.⁴ In a randomized study of scheduled versus as-needed FabAV dosing in patients whose symptoms were worsening, the Rocky Mountain Poison and Drug Center demonstrated a reduction in pain and other venom effects but noted a 20% acute and 23% delayed drug reaction.⁵
• Although copperhead bites are generally self-limiting, morbidity was reduced in moderate envenomation 4 hours after 4 vials of FabAV in 88% of cases. The cases that failed to respond were not changed by further FabAV doses.⁶
• FabAV is generally considered safe for children, as many of the studies did not discriminate in age. One large study from Mexico demonstrated no immediate or late allergic reactions to FabAV when administered according to grade of envenomation.³
• Give antivenin for coral snakebites as a standard of care if the patient presents within 12 hours of the bite, regardless of local or systemic signs. Neurotoxicity may develop without warning and lead to respiratory failure.
• Although FabAV helps control local tissue effects and hemotoxicity, aggressive antivenom therapy does not usually ameliorate neurotoxic effects such as myokymia (spontaneous, fine fascicular contractions of muscle without muscular atrophy or weakness) and major muscle fasciculations. The physician must maintain continuous monitoring of those patients with myokymia especially of the shoulders, chest, and diaphragm for the development of respiratory failure and need for mechanical ventilation.^7,8

Surgical Care

• Surgical assessment focuses on the injury site and concern for the development of compartment syndrome.
  • Fasciotomy is indicated only for those patients with objective evidence of elevated compartment pressure.
  • Liberal monitoring of compartment pressure is warranted. If this is not available, utilize the physical hallmark of compartment hypertension (pain with passive range of motion), along with distal pallor, paresthesia, or pulselessness for the clinical assessment.
• Tissue injury after compartment syndrome is not reversible but is preventable.

Consultations

• Contacting the poison control center is important.
• Consultation with a surgeon often is warranted in bite management. General and trauma surgeons often have experience with envenomation, resuscitation, complications, and wound care. They can lead the inpatient treatment.

Medication

The goals of pharmacotherapy are to neutralize the toxin, to reduce morbidity, and to prevent complications.

Antivenins

A neutralizing antibody gives antivenin efficacy. Two kinds of antivenin are available. One has been manufactured since 1956. It is derived from horse serum after the horse is injected with sublethal doses of snake venom (Wyeth). The antivenin is purified but still contains other serum proteins that can be immunogenic. The latest version, approved by the US Food and Drug Administration (FDA) in 2000 (CroFab, Savage), is a monovalent immunoglobulin fragment derived from sheep but purified to avoid other antigenic proteins.

The old antivenin may still be available, but it is generally recommended to use the more specific and purified drug. Even with the newer agent, one must remember while the antivenin may be life saving, it also may lead to immediate hypersensitivity (anaphylaxis) and delayed hypersensitivity (serum sickness) reactions and must be used with caution. To achieve maximum efficacy, administer within 4-6 hours of bite.

CroFab is made specifically from venom of the eastern and western diamondback snakes, Mohave rattlesnakes, and the cottonmouth/water moccasin snakes. The purpose of any antivenin is to bind the toxins in the venom and prevent both local and systemic results.

CroFab has been used in Crotalid bites with good effect (reduced fasciotomy) and reductions in antivenin toxicity. With this information, more liberal dosing may follow, certainly with Crotalids, possibly with copperheads.

Ovine Crotalidae polyvalent immune fab-purified (Crofab) FabAV

Affinity-purified, mixed monospecific Crotalidae antivenom. Used to neutralize toxins from snakebite.
Grading is dynamic, and requirements for antivenin may increase over time.
Reduced tissue injury and need for fasciotomy with no allergic consequences documented in one study.⁴ Study from the southwest United States and indigenous snakes include Crotalus species.
Most authors withhold antivenin for copperhead envenomations unless wound is particularly painful (early clue for significant envenomation).

Antibiotics

Antibiotics are often given upon arrival to hospital but most likely benefit only severe cases. However, broad-spectrum antibiotic prophylaxis is still recommended.

Ceftriaxone (Rocephin)

Third-generation cephalosporin with broad-spectrum gram-negative activity; lower efficacy against gram-positive organisms; higher efficacy against resistant organisms. Arrests bacterial growth by binding to one or more penicillin-binding proteins.

Immunizations

Snakes do not harbor Clostridium tetani in their mouths, but bites may carry other bacteria, especially gram-negative species. Tetanus prophylaxis is recommended if the patient is not immunized.

Diphtheria-tetanus toxoid (Decavac)

Used to induce active immunity against tetanus in selected patients. Immunizing agent of choice for most adults and children >7 y are tetanus and diphtheria toxoids. Necessary to administer booster doses to maintain tetanus immunity throughout life.
Pregnant patients should receive only tetanus toxoid not a product containing diphtheria antigen.
In children and adults, may administer into deltoid or midlateral thigh muscles. In infants, preferred site of administration is the mid thigh laterally.

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