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Snakebite Medication

  • Author: Brian J Daley, MD, MBA, FACS, FCCP, CNSC; Chief Editor: Joe Alcock, MD, MS  more...
Updated: Apr 08, 2016

Medication Summary

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



Class Summary

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.

Crotalidae polyvalent immune FAB (ovine) (Copperhead Antivenom (Immune FAB), Cottonmouth Antivenom (Immune FAB), CroFab)


Crotalidae polyvalent immune FAB is an affinity-purified, mixed monospecific Crotalidae antivenom. It is used to neutralize toxins from a snakebite. Grading is dynamic, and requirements for antivenin may increase over time.

It can reduce tissue injury and need for fasciotomy with no allergic consequences, as has been documented in one study. Most authors withhold antivenin for copperhead envenomations unless the wound is particularly painful (early clue for significant envenomation).



Class Summary

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)


Ceftriaxone is a third-generation cephalosporin with broad-spectrum gram-negative activity; it has lower efficacy against gram-positive organisms and higher efficacy against resistant organisms. Ceftriaxone arrests bacterial growth by binding to one or more penicillin-binding proteins.



Class Summary

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)


Diphtheria-tetanus toxoid is used to induce active immunity against tetanus in selected patients. The immunizing agents of choice for most adults and children older than 7 years are tetanus and diphtheria toxoids. It is necessary to administer booster doses to maintain tetanus immunity throughout life.

Pregnant patients should receive only tetanus toxoid, not a product containing the diphtheria antigen.

In children and adults, one may administer into the deltoid or midlateral thigh muscles. In infants, the preferred site of administration is the mid thigh laterally.

Contributor Information and Disclosures

Brian J Daley, MD, MBA, FACS, FCCP, CNSC Professor and Program Director, Department of Surgery, Chief, Division of Trauma and Critical Care, University of Tennessee Health Science Center College of Medicine

Brian J Daley, MD, MBA, FACS, FCCP, CNSC is a member of the following medical societies: American Association for the Surgery of Trauma, Eastern Association for the Surgery of Trauma, Southern Surgical Association, American College of Chest Physicians, American College of Surgeons, American Medical Association, Association for Academic Surgery, Association for Surgical Education, Shock Society, Society of Critical Care Medicine, Southeastern Surgical Congress, Tennessee Medical Association

Disclosure: Nothing to disclose.


Sneha Bhat, MD Resident Physician, Department of Surgery, University of Tennessee Health Science Center College of Medicine

Disclosure: Nothing to disclose.

Specialty Editor Board

Francisco Talavera, PharmD, PhD Adjunct Assistant Professor, University of Nebraska Medical Center College of Pharmacy; Editor-in-Chief, Medscape Drug Reference

Disclosure: Received salary from Medscape for employment. for: Medscape.

Daniel R Ouellette, MD, FCCP Associate Professor of Medicine, Wayne State University School of Medicine; Chair of the Clinical Competency Committee, Pulmonary and Critical Care Fellowship Program, Senior Staff and Attending Physician, Division of Pulmonary and Critical Care Medicine, Henry Ford Health System; Chair, Guideline Oversight Committee, American College of Chest Physicians

Daniel R Ouellette, MD, FCCP is a member of the following medical societies: American College of Chest Physicians, Society of Critical Care Medicine, American Thoracic Society

Disclosure: Nothing to disclose.

Chief Editor

Joe Alcock, MD, MS Associate Professor, Department of Emergency Medicine, University of New Mexico Health Sciences Center

Joe Alcock, MD, MS is a member of the following medical societies: American Academy of Emergency Medicine

Disclosure: Nothing to disclose.

Additional Contributors

Lisa Kirkland, MD, FACP, FCCM, MSHA Assistant Professor, Department of Internal Medicine, Division of Hospital Medicine, Mayo Clinic; Vice Chair, Department of Critical Care, ANW Intensivists, Abbott Northwestern Hospital

Lisa Kirkland, MD, FACP, FCCM, MSHA is a member of the following medical societies: American College of Physicians, Society of Hospital Medicine, Society of Critical Care Medicine

Disclosure: Nothing to disclose.

Chandler Long, MD Resident Physician, Department of Surgery, University of Tennessee Medical Center-Knoxville

Disclosure: Nothing to disclose.

A Mariah Alexander, MD Resident Physician, Department of Surgery, University of Tennessee Graduate School of Medicine, Knoxville

A Mariah Alexander, MD is a member of the following medical societies: American College of Surgeons, Society of American Gastrointestinal and Endoscopic Surgeons

Disclosure: Nothing to disclose.

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Snakebite. Western diamondback rattlesnake.
Snakebite. Western coral snake.
Snakebite. Southern Copperhead snake, from
Snakebite. Copperhead bite day 3; initial wounds to finger.
Snakebite. Copperhead bite day 3; initial wounds to finger.
Snakebite. Copperhead bite day 3; initial wounds to finger.
Snakebite. Comparison of the harmless Lampropeltis triangulum annulata (Mexican milksnake) (top) with Micrurus tener (Texas coral snake) (bottom). Photo by Charles Alfaro.
Snakebite. Juvenile southern Pacific rattlesnake (Crotalus oreganus helleri). Photo by Sean Bush, MD.
Snakebite. Moderate rattlesnake envenomation in a toddler after treatment with antivenom. Photo by Sean Bush, MD.
Table 1. Snakebite Severity Scale
Criteria Signs/Symptoms Score
  No symptom/sign 0
  Dyspnea, minimal chest tightness, mild or vague discomfort, or respirations of 20-25 breaths/min 1
  Moderate respiratory distress (tachypnea, 26-40 breaths/min, accessory muscle use) 2
  Cyanosis, air hunger, extreme tachypnea, or respiratory insufficiency/failure 3
  No symptom/sign 0
  Tachycardia (100-125 beats/min), palpitations, generalized weakness, benign dysrhythmia, or hypertension 1
  Tachycardia (126-175 beats/min) or hypotension with systolic blood pressure < 100 mm Hg 2
  Extreme tachycardia (>175 beats/min) or hypotension with systolic blood pressure < 100 mm Hg, malignant dysrhythmia, or cardiac arrest 3
Local wound No symptom/sign (swelling or erythema < 2.5 cm of fang mark) 0
  Pain, swelling, or ecchymosis within 5-7.5 cm of bite site 1
  Pain, swelling, or ecchymosis involving less than half of the extremity (7.5 cm from site) 2
  Pain, swelling, or ecchymosis extending beyond affected extremity (>100 cm from site) 3
  No symptom/sign 0
  Pain, tenesmus, or nausea 1
  Vomiting or diarrhea 2
  Repeated vomiting or diarrhea, hematemesis, hematochezia 3
  No symptom/sign 0
  Coagulation parameters slightly abnormal (PTa < 20 seconds, PTTb < 50 seconds, platelets 100,000-150,000/µL, fibrinogen 100-150 mcg/mL) 1
  Coagulation parameters abnormal (PT < 20-50 seconds, PTT < 50-75 seconds, platelets 50,000-100,000/µL, fibrinogen 50-100 mcg/mL) 2
  Coagulation parameters abnormal (PT < 50-100 seconds, PTT < 75-100 seconds, platelets 20,000-50,000/µL, fibrinogen < 50 mcg/mL) 3
  Coagulation parameters markedly abnormal, with serious bleeding or threat of spontaneous bleeding (PT or PTT unmeasurable, platelets < 20,000/µL, fibrinogen undetectable), with severe abnormalities in other laboratory values, including venous clotting time 4
Central nervous system    
  No symptom/sign 0
  Minimal apprehension, headache, weakness, dizziness, chills, or paresthesia 1
  Moderate apprehension, headache, weakness, dizziness, chills, paresthesia, confusion, or fasciculation in area of bite site, ptosis, and dysphagia 2
  Severe confusion, lethargy, seizure, coma, psychosis, or generalized fasciculation 3
  Extremely severe envenomation leading to death 4
a PT = Prothrombin time.

b PTT = Partial thromboplastin time.

Table 2. Severity of Envenomation
Type of Signs/Symptoms Minimal Moderate Severe
Local Swelling, erythema, or ecchymosis confined to bite site Progression of swelling, erythema, or ecchymosis beyond bite site Rapid swelling, erythema, or ecchymosis involving the entire body part
Systemic No systemic signs or symptoms Non–life-threatening signs or symptoms (nausea/vomiting, mild hypotension, perioral paresthesias, myokymia) Markedly severe signs or symptoms (hypotension [systolic < 80 mm Hg], altered sensorium, tachycardia, tachypnea, and respiratory distress)
Coagulation No coagulation abnormalities or other laboratory abnormalities Mild abnormal coagulation profile without significant bleeding Abnormal coagulation profile with bleeding (INRa, aPTTb, fibrinogen, platelet count < 20,000/µL
Snakebite Severity Score 0-3 4-7 8-20
a INR = International normalized ratio.

b aPTT = Activated partial thromboplastin time.

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