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Snake Envenomation, Moccasins: Treatment & Medication
Updated: Jul 24, 2008
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
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Treatment
Prehospital Care
Do nothing to injure the patient or impede travel to the ED.
- Support the airway, breathing, and circulation per advanced cardiac life support (ACLS) protocol with oxygen, monitors, large-bore intravenous lines, and fluid challenge. Minimize activity (if possible), remove jewelry or tight-fitting clothes in anticipation of swelling, and transport the patient to the ED as quickly and as safely as possible. Every 15 minutes, use a pen to mark and time the border of advancing edema.
- In recent studies, no benefit was demonstrated when a negative pressure venom extraction device (eg, The Extractor from Sawyer Products) was evaluated; additional injury can result. Incision across fang marks is not recommended. Mouth suction is contraindicated.
- Lymphatic constriction bands and pressure immobilization techniques may inhibit the spread of venom, but whether they improve outcome is not clear. These techniques may actually be deleterious for pit viper envenomation if they increase local necrosis or compartment pressure. Tourniquets are not recommended.
- Maintain the limb in a neutral position.
- First aid that lacks therapeutic value or is potentially more harmful than the snakebite includes electric shock, alcohol, stimulants, aspirin, ice application, and various folk and herbal remedies.
- Cost and risk of acute adverse reactions generally preclude field use of antivenom.
- Attempts to capture or kill the snake are not recommended because of the risk of additional injury.
- In the United States, all pit viper (rattlesnake, pygmy rattlesnake, and moccasin) envenomations are treated similarly, based on the severity of presenting signs and symptoms. Therefore, if the patient shows signs of envenomation (eg, pain, swelling), then species identification is not necessary. The exception to this rule is Mohave rattlesnakes, whose neurotoxic venom requires special consideration. However, because there is little overlap between the natural range of Mohave rattlesnakes and that of the moccasins (except for the Trans-Pecos region of Texas), this is rarely a clinical dilemma.
- If the venomousness of a particular snake is uncertain, consider taking photographs of the snake from a safe distance of at least 6 feet away using a digital or Polaroid camera.
Emergency Department Care
Adequate hydration with intravenous fluids is indicated. Patients with hypotension should be resuscitated first with 2 isotonic sodium chloride solution challenges (eg, 20 mL/kg). Treat persistent shock with colloids, followed by pressors as indicated.
Grading envenomations is a dynamic process; administer additional antivenom as indicated by a worsening clinical course. When considering the use of antivenom, the risk of allergy to antivenom must be weighed against the benefits of reducing venom toxicity.
- Nonenvenomation (ie, dry bite)
- Local effects - Puncture wounds only
- Systemic effects - None
- Coagulation abnormalities - No laboratory evidence of coagulation abnormalities and no clinical evidence of abnormal bleeding or clotting
- Minimal or mild envenomation
- Local effects - Swelling, pain, tenderness, and/or ecchymosis confined to the immediate bite area
- Systemic effects - None
- Coagulation abnormalities - No laboratory evidence of coagulation abnormalities and no clinical evidence of abnormal bleeding or clotting
- Moderate envenomation
- Local effects - Swelling, pain, tenderness, and/or ecchymosis extending beyond the immediate bite area, but involving less than the entire extremity.
- Systemic effects - Present but not life threatening; may include nausea, vomiting, oral paresthesias or unusual tastes, fasciculations (myokymia), moderate tachycardia (heart rate <150 bpm), and tachypnea
- Coagulation abnormalities - Laboratory evidence of coagulation abnormalities and thrombocytopenia, such as elevated PT, or PTT and decreased fibrinogen or platelet counts may be present, but no clinical evidence of abnormal bleeding or clotting exists.
- Severe envenomation
- Local effects - Swelling, pain, tenderness, and/or ecchymosis extending beyond the entire extremity or threatening the airway, or proven compartment syndrome.
- Systemic effects - Shock or significant hypotension, altered mental status, severe tachycardia or tachypnea, respiratory insufficiency, and/or severe altered mental status
- Coagulation abnormalities - Marked abnormalities of PT, PTT, fibrinogen, or platelets, possibly associated with serious bleeding
Consultations
- In the United States, the nationwide Poison Help! number, 1-800-222-1222 will connect the caller the nearest poison control center. Certified poison centers have trained personnel to assist physicians in the management of poisonings, including snake bites, with 24-hour access to medical toxicologists for specific questions.
- In addition, medical toxicologists are available to provide bedside patient care at some medical centers. Medical toxicologists have specific training and expertise in snakebite management.
- The manufacturer of Crotaline Fab antivenom provides a technical assistance hotline at 1-877-SERPDRUG (877-377-3784).
- Consider consulting a surgeon (eg, general, orthopedic, hand) if compartment syndrome is suspected or, in the subacute phase of illness, if debridement of clearly necrotic tissue is required.
- Occupational therapy, physical therapy, physiatry (rehabilitative medicine), and/or pain management consultation may be helpful to assist patients with persistent pain, swelling, or other limitations.
Medication
The physician must be prepared to support the patient's cardiovascular and respiratory systems after any venomous snakebite.
Antivenom
This agent neutralizes toxins from snakebites. Two antivenoms are available: Crotaline Fab antivenom (CroFab) and Antivenin Crotalidae Polyvalent.
Crotaline Fab antivenom (CroFab; Crotaline immune Fab (ovine), Protherics, Nashville, TN) is a highly purified product derived from sheep hyperimmunized with the venom of 4 crotaline snakes, including Agkistrodon piscivorus. A relatively pure IgG fraction is extracted from the sheep serum and cleaved with papain to remove the antigenic Fc portion. Column affinity purification is then used to produce product consisting almost entirely of Fab fragments with specific affinity to snake venom.
Equine antivenom (Antivenin (Crotalidae) Polyvalent, Wyeth, Marietta, PA) is a whole IgG antivenom produced by immunizing horses with 3 North American rattlesnakes and a Central American snake, the Fer-de-lance. In recent years, production of equine antivenom has been intermittent; whether this product will continue to be produced in the future is uncertain. For further information on Crotalidae, see the prescribing information.
Both antivenoms are associated with acute and delayed allergic reactions. However, both the incidence and the severity of these reactions are greater with equine antivenom than with crotaline Fab antivenom.
Urticaria occurs in 12-29% of patients, and anaphylaxis occurs in 2-15% of patients who receive equine antivenom. The incidence of serum sickness depends on the antivenom dose administered and ranges from 20-50% of patients who received equine antivenom in published series. Two deaths due to anaphylactic reactions to equine antivenom have been reported in the United States.
In contrast, urticaria has been reported in approximately 8% of patients treated with crotaline Fab antivenom; wheezing is reported in 2% and serum sickness in less than 10%. No deaths have been reported, and almost all patients have been able to complete antivenom therapy after treatment of mild allergic reactions.
This difference in safety may lead to a change in the standard management of mild-to-moderate moccasin envenomation. Historically, only 8% of copperhead victims were treated with equine antivenom. However, because crotaline Fab antivenom appears to be safer to administer than equine antivenom, the threshold for Fab antivenom administration may be lower than for equine antivenom. However, the cost of therapy is significant, and cost-benefit analysis is not available.
Unlike equine antivenom, Crotaline Fab antivenom has not been approved by the FDA for treatment of severe envenomation. However, significant clinical experience, including published case series, supports the role of Crotaline Fab antivenom in severe envenomations.
Crotaline Fab antivenom has been formally tested in humans envenomated by cottonmouth snakes (Agkistrodon piscivorus), but not in humans envenomated by copperheads (A contortrix). However, a large retrospective case series supports the effectiveness of Fab antivenom in treatment of copperhead bites.
Crotaline Fab antivenom appears to be less effective than equine antivenom in correcting severe coagulopathy and thrombocytopenia. Although correction is sometimes not complete, the correction obtained by Fab antivenom administration is generally adequate to stop systemic bleeding. However, administration of equine antivenom may be useful in cases of ongoing hemorrhage that do not respond to Fab antivenom. This problem is extremely rare with moccasin envenomations. For further information on CroFab, see the prescribing information.
Another antivenom (Antivipmyn, manufactured by Instituto Bioclon) has been FDA approved for experimental use and is currently undergoing phase III clinical trials.
CroFab (Crotalidae Polyvalent Immune Fab Ovine)
Appears to be more specific against moccasin venom and less allergenic than Antivenin (Crotalidae) Polyvalent.
Adult
Not for use in nonenvenomations
Minimal envenomation: 4 vials if signs of envenomation progressive
Moderate envenomation: 4 vials if signs of envenomation progressing
Severe envenomation: 6 vials and more as indicated by envenomation progression
Preparing infusion: Reconstitute each vial with 10 mL of warmed sterile water; mix dose of antivenom in normal saline to total volume 250 mL
Administration: Although risk of severe allergic reaction low, administer first dose with antihistamines, epinephrine, airway equipment, and qualified personnel immediately available; begin infusion at 50 mL/h, and observe patient for signs of allergic reaction
If no evidence of allergic reaction, increase infusion rate to 250 mL/h until completion
Repeat above doses prn until control of envenomation syndrome (swelling no longer progressing; blood pressure acceptable; systemic bleeding halted; coagulation parameters and platelet count improving) achieved
Maintenance therapy: Indicated in cases involving severe envenomation, coagulopathy, or thrombocytopenia; dose is two vials IV in 100 mL NS q6h for 18 h (3 doses)
Additional 2-vial doses may be administered prn on basis of patient's clinical course (eg, for recurrent progressive swelling or coagulopathy)
Pediatric
Administer as in adults; may need to decrease fluid volumes in children <20 kg
Not established
Documented hypersensitivity to ovine antivenom, sheep, papain, or latex; previous exposure to CroFab not a contraindication; in severe cases, previous allergic reaction to CroFab not a contraindication (prepare and use prudent consideration of risks and benefits)
Pregnancy
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions
Because of low molecular weight of Fab antivenom, some patients will develop recurrent venom effects (swelling, coagulopathy, or thrombocytopenia) after initially successful control of envenomation by Fab antivenom (treat clinically significant recurrence with repeat doses of antivenom; coagulopathy, may recur up to 2 wk after envenomation); role of antivenom in treatment of asymptomatic delayed coagulopathy not established
Antivenin (Crotalidae) polyvalent
Because moccasin envenomations are usually milder than those inflicted by rattlesnakes and because of the potentially severe adverse reactions associated with this product, use is generally contraindicated except as last resort.
Adult
Not for use in nonenvenomations or minimal envenomations
Moderate envenomation: 10 vials and repeat prn if signs of envenomation progress rapidly
Severe envenomation: 20-30 vials followed by 10-20 vial doses prn
Preparation of infusion: Reconstitute each vial in 10 mL of warm saline by using gentle agitation (not shaking; powder may take 20-90 min to dissolve) further dilute 10 dissolved vials into total dilution of 200-250 mL normal saline
Administration: As noted above, skin testing has limited value in determining which patients will develop acute allergic reactions to equine antivenom (procedure for skin testing is listed above, in Other Tests); do not delay administration of antivenom to perform skin testing in cases of severe envenomation
Because severe allergic reactions, including fatal anaphylaxis have been reported, administer initial dose of equine antivenom in a setting where definitive airway management is possible
Although not mandatory, premedication with antihistamine (eg, diphenhydramine) is prudent; some experienced clinicians prepare an epinephrine drip to have at bedside during equine antivenom administration; pretreatment with steroids is unlikely to prevent immediate reactions but may be helpful later if continued antivenom is indicated despite allergic reaction
Airway equipment, including surgical airway equipment, and physicians skilled at its use should be present when first dose of equine antivenom initiated
Start infusion at 10 mL/h for 10 min, closely monitoring for signs of allergic reaction; if no allergic reaction occurs, increase rate to complete infusion over 1 h; in children, run infusion at 10 mL/kg/h
Repeat above doses prn until control of envenomation syndrome (swelling no longer progressing; blood pressure acceptable; systemic bleeding halted; coagulation parameters and platelet count improving) achieved
May administer additional 10-20 vial doses prn on the basis of patient's clinical course
Pediatric
Administer as in adults
None reported
Documented hypersensitivity to horse serum, previous administration of equine serum, or positive skin test reaction; administration contraindicated unless envenomation is severe and alternative antivenoms (eg, ovine antivenom) not available
Pregnancy
B - Fetal risk not confirmed in studies in humans but has been shown in some studies in animals
Precautions
Because of presence of horse serum, agents for emergency treatment of anaphylaxis should be available as explained above
Immunizations
Immunize patients against tetanus.
Diphtheria-tetanus toxoid (dT)
Used to induce active immunity against tetanus in selected patients. Tetanus and diphtheria toxoids are the immunizing agents of choice for most adults and children >7 y. Booster doses are necessary to maintain tetanus immunity throughout life because tetanus spores are ubiquitous.
Pregnant patients should receive only tetanus toxoid, not a diphtheria antigen–containing product. In children and adults, immunization may be administered into the deltoid or midlateral thigh muscles. In infants, the preferred site of administration is the mid thigh laterally.
Adult
Primary immunization: 0.5 mL IM; administer 2 injections 4-8 wk apart and a third dose 6-12 mo after the second injection
Booster dose: 0.5 mL IM q10y
Pediatric
Administer as in adults
Patients receiving immunosuppressants, including corticosteroids or radiation therapy, may remain susceptible despite immunization because of poor immune response; cimetidine may enhance or augment delayed-hypersensitivity responses to skin-test antigens; avoid concurrent use of medication with systemic chloramphenicol because it may impair amnestic response to tetanus toxoid; concurrent use of tetanus immune globulin may delay development of active immunity by several days (nevertheless, interaction is clinically insignificant and does not preclude its concurrent use)
Documented hypersensitivity; a history of any type of neurologic symptoms or signs following administration of this product; FDA recommends that elective tetanus immunization be deferred during any outbreak of poliomyelitis because tetanus toxoid injections are an important cause of provocative poliomyelitis
Pregnancy
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions
Do not use to treat actual tetanus infections or for immediate prophylaxis of unimmunized individuals (use tetanus antitoxin instead, preferably human tetanus immune globulin); diminished antibody response to active immunization may be observed in patients receiving immunosuppressive therapy; better to defer primary diphtheria immunization until immunosuppressive therapy discontinued; routine immunization of symptomatic and asymptomatic HIV-infected persons is recommended
Hematologic agents
Consider transfusion, in conjunction with ongoing antivenom administration, if antivenom alone does not correct severe coagulopathy or patient has active severe bleeding. Transfusion is generally recommended for life-threatening bleeding (rare), platelets <20,000 mm3, or hemoglobin <7 g/dL. Use transfusion as temporizing measure only after adequate antivenom therapy because antivenom may correct coagulopathies more definitively. Coagulopathy often recurs and may persist for as long as 2 weeks after envenomation.
Platelets, fresh frozen plasma (FFP), and packed RBCs (PRBCs)
These agents are preferred initially to whole blood because they limit volume, immune, and storage complications. PRBCs have 80% less plasma, are less immunogenic, and can be stored about 40 d (vs 35 d for whole blood). PRBCs are obtained after centrifugation of whole blood. Leukocyte-poor PRBCs are used in patients who are transplant candidates/recipients or in those with prior febrile transfusion reactions. Washed or frozen PRBCs are used in individuals with hypersensitivity transfusion reactions.
Adult
1 U of PRBCs should raise hemoglobin by 1 g/dL or hematocrit by 3%; blood can be administered over 3-4 h IV, premedicating with acetaminophen and diphenhydramine to prevent febrile transfusion reactions
Pediatric
10 mL/kg IV bolus if whole blood (preferred)
5 mL/kg IV bolus if PRBCs used
None reported
Refusal of blood product by a competent adult or a legal guardian of a minor can create a difficult situation; immediate consultations with hospital ethical and legal staff strongly recommended
Pregnancy
C - Fetal risk revealed in studies in animals but not established or not studied in humans; may use if benefits outweigh risk to fetus
Precautions
In transfusion reactions, transmission of blood-borne pathogens may be of concern
More on Snake Envenomation, Moccasins |
| Overview: Snake Envenomation, Moccasins |
| Differential Diagnoses & Workup: Snake Envenomation, Moccasins |
 Treatment & Medication: Snake Envenomation, Moccasins |
| Follow-up: Snake Envenomation, Moccasins |
| Multimedia: Snake Envenomation, Moccasins |
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References
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Thorson A, Lavonas EJ, Rouse AM, Kerns WP 2nd. Copperhead envenomations in the Carolinas. J Toxicol Clin Toxicol. 2003;41(1):29-35. [Medline].
Whitley RE. Conservative treatment of copperhead snakebites without antivenin. J Trauma. Aug 1996;41(2):219-21. [Medline].
Wingert WA, Pattabhiraman TR, Cleland R, Meyer P, Pattabhiraman R, Russell FE. Distribution and pathology of copperhead (agkistrodon contortrix) venom. Toxicon. 1980;18(5-6):591-601. [Medline].
Bronstein AC, Spyker DA, Cantilena LR Jr, Green J, Rumack BH, Heard SE. 2006 Annual Report of the American Association of Poison Control Centers' National Poison Data System (NPDS). Clin Toxicol (Phila). Dec 2007;45(8):815-917. [Medline].
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Further Reading
Keywords
moccasin snake bite , moccasin snake envenomation , pit viper snake bite, moccasin venom, snake bite, Agkistrodon genus, cottonmouth, Agkistrodon piscivorus, copperhead, Agkistrodon contortrix, cantil, Agkistrodon bilineatus, mamushi, Agkistrodon blomhoffii, Siberian pit viper, Agkistrodon halys, Central Asian pit viper, Agkistrodon intermedius, Malayan pit viper, Calloselasma rhodostoma, hundred-pace snake, Deinagkistrodon acutus
