AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

• Authors and Editors
• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

INTRODUCTION

Section 2 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
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Background

Moccasins are new world pit vipers (family Viperidae, subfamily Crotalinae), which may be identified by a heat-sensing pit anteroinferior to each eye, elliptical pupils, a triangular head, and undivided subcaudal scales.

Moccasins comprise the genus Agkistrodon, which includes the cottonmouth (Agkistrodon piscivorus) and copperhead (Agkistrodon contortrix) in the southeastern United States; the cantil (Agkistrodon bilineatus) in Mexico and Central America; the mamushi (Agkistrodon blomhoffii), Siberian pit viper (Agkistrodon halys), and Central Asian pit viper (Agkistrodon intermedius) in central and northeastern Asia; and the Malayan pit viper (Calloselasma rhodostoma) and hundred-pace snake (Deinagkistrodon acutus) in southeastern Asia.

Pathophysiology

Envenomation occurs when the moccasin injects venom via hollow movable fangs located in the anterior mouth. The effects of moccasin envenomation are generally similar to rattlesnake envenomation. However, in most cases, moccasin envenomation is less serious than envenomation by rattlesnakes. For further discussion of more severe pit viper envenomation, see Snake Envenomations, Rattle.

Moccasin venom is complex, with nearly 50 identified components. These can be broken down into 4 major categories:

• Proteolytic enzymes that directly destroy tissue, as happens in digestion of prey animals
• Inflammatory mediators, including histamine- and bradykinin-like factors, that cause pain, erythema, swelling, and occasionally distributive shock
• Fibrinolytic enzymes that cleave fibrin into ineffective D-dimers, resulting in coagulopathy
• Antiplatelet factors that cause thrombocytopenia

Although neurotoxic factors can be detected in moccasin venom, clinically significant neurotoxicity does not occur with envenomation by copperheads or cottonmouths.

Frequency

United States

Approximately 5,000 snakebites are reported to poison centers each year. Of the venomous snakebites for which the species is known, moccasins are responsible for 42%. The vast majority of these (86%) are copperhead envenomations. In portions of the southeastern United States, copperheads account for 85% of all reported snake envenomations.

International

An estimated 300,000-400,000 venomous snakebites occur per year worldwide. The proportion of these caused by Agkistrodon species is not known.

Mortality/Morbidity

The American Association of Poison Control Centers (AAPCC) has reported only one death from moccasin envenomation since its first annual report in 1983. Prospective studies of morbidity from moccasin envenomation have not been conducted. However, in two retrospective studies of copperhead victims, patients missed a median of 2 or 6 weeks of work.

Sex

Incidence of snakebite is higher in males than in females.

Age

Young adults are bitten most commonly.

CLINICAL

Section 3 of 11  

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• Introduction
• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

History

• Most bites occur on the extremities. Upper extremity bites predominate in males and are often associated with deliberate handling of the snake.
• Pain around the bite site
• Swelling
• Nausea, vomiting, or diarrhea
• Syncope, near syncope
• Co-intoxication with alcohol is common and may affect the patient's judgment and ability to comply with therapy.

Physical

Although moccasin envenomation usually is associated with less severe local effects than rattlesnake envenomation, severe envenomations do occur.

• Fang marks are common, but they may be absent.
• Hemorrhagic vesicles may be present at the envenomation site.
• Tenderness surrounding bite site is almost always present.
• Local edema
• • Use a pen to mark and time the border of advancing edema and tenderness often enough to gauge progression.
  • Circumferential measurements of the envenomated extremity, repeated over time, may help differentiate swelling that is progressing (getting worse) from swelling that has stabilized (improving or not getting worse) but for which the leading edge is moving proximally because of limb elevation (see Image 4). Measurements of the contralateral (uninvolved) extremity may be useful for comparison.
  • Rapidly progressive swelling is usually indicative of a more severe envenomation.
• Erythema at the bite site, proximal to the bite site, and along patterns of lymphatic drainage
• Ecchymosis
• Bullae
• Bleeding into the tissues of the bite site is common. Systemic bleeding is uncommon in moccasin envenomations, occurring in less than 5% of copperhead envenomations.
• Tachycardia is common and due to pain, anxiety, and third-spacing of fluids due to inflammation.
• Hypotension is uncommon and usually due to intravascular volume depletion.

Causes

A large percentage of bites are considered intentionally interactive—they occur when the snake is handled, kept as a pet, or abused. Many bites are associated with ethanol use.

DIFFERENTIALS

Section 4 of 11  

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• Clinical
• Differentials
• Workup
• Treatment
• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

WORKUP

Section 5 of 11  

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• Workup
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• Medication
• Follow-up
• Miscellaneous
• Multimedia
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Lab Studies

• Coagulopathy and thrombocytopenia may occur with pit viper envenomation. However, these problems are much less common after moccasin envenomations than after rattlesnake envenomations. Numeric coagulopathy and/or thrombocytopenia occur in approximately 10% of copperhead envenomations; clinically significant bleeding occurs in less than 5%. For a more detailed discussion of coagulopathy induced by pit viper venom, see Snake Envenomations, Rattle.
• • CBC including platelet count
  • PT
  • Activated partial thromboplastin time (aPTT)
  • Fibrinogen
  • Type and screen, only if severe coagulopathy/thrombocytopenia are present or clinical bleeding is suspected.
• Additional laboratory and other diagnostic data should be obtained on a case-by-case basis. Factors to consider may include severity of envenomation, physician preference, and cost.
• • Bacterial cultures are rarely helpful. The incidence of infection in these envenomations is approximately 2%.
  • Patients who develop shock, respiratory failure, or signs suggesting rhabdomyolysis may benefit from measurements of electrolytes, BUN, creatinine, creatine phosphokinase (CPK), and arterial blood gases, on a case-by-case basis.

Imaging Studies

• Plain radiographs may depict teeth or fangs retained in wound. However, this finding is uncommon; routine radiography is not recommended.

Other Tests

• Skin testing for allergy to antivenom
• • Skin testing is not necessary prior to administration of ovine Fab antivenom (CroFab).
  • The manufacturer of equine whole IgG antivenom (Antivenin (Crotalidae) Polyvalent) recommends skin testing prior to antivenom administration and provides a vial of horse serum for this purpose. However, experts disagree about whether this test is necessary or helpful.
    • If skin testing is to be performed, first prepare for possible allergic reaction. Antihistamines, epinephrine, intubating equipment, and qualified personnel should be present and immediately available when skin testing is performed and when equine antivenom is administered.
    • Dilute 0.02-0.03 mL of horse serum or reconstituted equine antivenom in a 1:10 dilution with normal saline. Inject the entire amount (0.2-0.3 mL) subcutaneously.
    • A positive test result is manifested by the development of a wheal within 5-30 minutes.
    • Skin testing may be considered variably useful in predicting immediate hypersensitivity in cases of moderate envenomation when it is uncertain if the need for antivenom outweighs the risk of anaphylaxis. However, skin testing is unreliable. False-positive and false-negative results may occur.
    • If antivenom is clearly indicated, begin administration as described below, without waiting to conduct a skin test.
    • Using antivenom rather than the horse serum control that is supplied may increase the sensitivity and specificity of the test.
    • Skin testing may sensitize individuals at risk for future exposures to antivenom, or it may precipitate anaphylaxis.
• Electrocardiogram because moccasin venom is not cardiotoxic, routine examination of the electrocardiogram is not required. An ECG may be useful in cases of shock.

Procedures

• Fasciotomy is rarely indicated in cases of moccasin envenomation.
• • Because envenomation produces limb swelling, severe pain, and pain with passive stretch, it is common for envenomated limbs to appear similar to limbs with compartment syndrome. However, true compartment syndrome is present in less than 2% of moccasin envenomations.
  • Compartment pressure monitoring is indicated in cases of suspected compartment syndrome.
  • The preferred therapy for compartment syndrome due to moccasin envenomation is administration of antivenom.
    • Crotaline Fab antivenom has been shown to improve perfusion pressures in an animal model and in human case reports.
    • Fasciotomy should be reserved for cases in which compartment pressures remain elevated despite administration of adequate doses of antivenom, or in cases of compartment syndrome when antivenom cannot be obtained.
  • Because tissue pressures in the fingers and toes cannot be measured accurately, the diagnosis of suspected compartment syndrome in the digits is difficult.
    • If capillary refill is poor, administer antivenom to reduce swelling and attempt to restore perfusion.
    • If capillary refill remains poor after administration of adequate doses of antivenom, digit dermotomy may be indicated.

TREATMENT

Section 6 of 11  

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• Follow-up
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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

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The physician must be prepared to support the patient's cardiovascular and respiratory systems after any venomous snakebite.

Drug Category: 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 II clinical trials.

Drug Name	Antivenin (Crotalidae) polyvalent
Description	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 Dose	Not for use in nonenvenomations or minimal envenomations Moderate envenomation: 10 vials and repeat prn if signs of envenomation progress rapidlySevere 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 Dose	Administer as in adults
Contraindications	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
Interactions	None reported
Pregnancy	B - Usually safe but benefits must outweigh the risks.
Precautions	Because of presence of horse serum, agents for emergency treatment of anaphylaxis should be available as explained above

Drug Category: Immunizations

Immunize patients against tetanus.

Drug Category: 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.

FOLLOW-UP

Section 8 of 11  

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Further Inpatient Care

• Patients believed to have dry bites, in which no venom effects develop, should be observed for at least 8 hours. Close follow-up and/or recheck examination is recommended.
• Patients who have minimal envenomation may be admitted for overnight observation, or they may be discharged if signs of envenomation do not progress for at least 8 hours.
• Patients whose envenomation is severe enough to require antivenom should be admitted.
• Several reports in the literature have documented instances in which patients who were initially discharged with a mild envenomation returned in several hours with significant injury and required antivenom and admission. However, because the denominator (patients who go home with no progression) is not known, it is unclear whether the strategy of admitting all patients with mild envenomation is cost-effective.
• Regardless of the period of observations, patients who are discharged should be instructed to return to the hospital if pain or swelling increase or if new symptoms develop. Because patients at home rarely elevate their envenomated limbs consistently, some increase in swelling is expected during the first 1-3 days after the patient goes home. If not accompanied by increasing pain or other signs/symptoms, this is not a concern.

Further Outpatient Care

• Discharge instructions should include the following:
• • Keep the envenomated extremity elevated.
  • Return immediately if swelling worsens or pain becomes severe.
  • Return immediately if any abnormal bleeding or bruising, dark tarry stools, or severe headache occurs.
  • Return for signs of wound infection, such as fever, worsening redness, or swelling immediately adjacent to the bite site, or drainage of pus. Because tenderness at the bite site, more generalized swelling, and lymphangitic streaking are common manifestations of the envenomation itself, these are less useful as signs of infection.
  • Return or follow up if a fever, itchy rash, joint pain, or swollen lymph nodes occur any time during the next few weeks.
  • Do not take nonsteroidal anti-inflammatory drugs (NSAIDs), such as aspirin, ibuprofen (Motrin, Advil), or naproxen (Naprosyn, Aleve) for 2 weeks after the snakebite. Acetaminophen (Tylenol) or a prescribed pain medication can be taken.
  • Do not participate in contact sports, undergo elective surgery, or have dental work for 2 weeks after the snakebite.
  • Drink plenty of liquids. Return if urine decreases in amount or becomes cola colored.
  • Referral to a physical therapist or surgeon may be indicated.
  • Patients who developed severe coagulopathy or thrombocytopenia should have these studies rechecked in 3 days, and as needed for signs of coagulation problems (eg, bleeding gums, easy bruising).

In/Out Patient Meds

• Administer antihistamines and steroids if serum sickness to antivenom develops.
• Short courses of opioid pain medications are often required.

Transfer

• If indicated, patients may require transfer after stabilization to a facility where antivenom can be administered.

Deterrence/Prevention

• Never handle a rattlesnake, even if it is believed to be dead.
• Do not reach or step into places outdoors that are not visible.
• At home, remove debris in which snakes might hide (eg, log piles). Remove items, such as bird feeders, that might attract snakes—seeds that fall from bird feeders attract rodents, which attract snakes.
• Heavy clothing (such as hiking boots) may retard some strikes.
• Young children should be closely supervised, and older children should be educated to avoid snakes.

Complications

• Bleeding
• Compartment syndrome
• Skin and soft tissue necrosis
• Rhabdomyolysis
• Infection
• Death
• Antivenom-associated complications
• • Immediate hypersensitivity reactions
    • Anaphylaxis is a type I (immediate) hypersensitivity reaction, which may be life threatening.
    • Anaphylactoid reactions are histamine release stimulated by rapid infusion of medications, such as antivenom, that do not involve immune system sensitization.
    • Both anaphylactic and anaphylactoid reactions may be characterized by urticaria, airway swelling, wheezing, and shock. Anaphylactoid reactions are related to the rate of infusion; anaphylactic reactions are not related to rate or dose.
    • Urticaria occurs in approximately 8% of patients treated with crotaline Fab antivenom and in 12-29% of patients who receive equine antivenom. More severe reactions such as wheezing and hypotension occur in approximately 2% of Fab antivenom-treated and in 2-15% of equine antivenom-treated patients.
    • Immediate hypersensitivity is treated by halting the infusion and administering antihistamines, steroids, and epinephrine as needed. If continued antivenom therapy is necessary, it is often possible to complete the antivenom infusion, after appropriate therapy, at a slower rate.
  • Delayed hypersensitivity reactions: Urticaria occurs in 12-29% of patients and anaphylaxis 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%.
    • Serum sickness is a type III (delayed) hypersensitivity reaction.
    • Serum sickness is characterized by fever, urticaria or petechial rash, lymphadenopathy, and arthritis, that may occur 5 days to 3 weeks after antivenom administration. Although serum sickness is uncomfortable, it is usually benign and self-limited.
    • Serum sickness occurs in less than 10% of patients who receive crotaline Fab antivenom and in 20-50% of patients treated with equine antivenom. Antivenin (Crotalidae) Polyvalent administration in as many as 50% of patients. Serum sickness is dose-related and almost always occurs when more than 8 vials of Antivenin (Crotalidae) Polyvalent are administered.

Prognosis

• Nearly all patients fully recover after moccasin envenomation.
• Some patients have long-term problems with limb pain and/or swelling, particularly after physical exertion. The proportion of patients that develop these sequelae and the impact of antivenom therapy on this incidence are not known.

Patient Education

• Call professionals, such as animal control, to move snakes.
• Never attempt to handle, possess, or kill venomous reptiles.
• For excellent patient education resources, visit eMedicine's Bites and Stings Center. Also, see eMedicine's patient education article Snakebite.

MISCELLANEOUS

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• Miscellaneous
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Medical/Legal Pitfalls

• Medicolegal problems may occur when a patient is sent home with a diagnosis of mild or no envenomation but subsequently returns with significant envenomation and requires antivenom and/or admission.
• Failure to treat with antivenom, when indicated, is a pitfall. Adverse outcomes from allergic reaction to antivenom have also resulted in legal action against physicians.
• Delays from the time the patient seeks medical care and the time the patient is treated are often cited in litigation.
• If possible, obtain informed consent before administering antivenom.
• Inform the patient that loss of tissue or function may result from moccasin envenomation and that antivenom and/or surgery may not prevent it.

Special Concerns

• Envenomation is an uncommon occurrence with an extremely variable presentation, ranging from no ill effects to multisystem failure and death.
• Treatment of envenomation is often based on speculation and anecdote, and much of the literature is contradictory. The authors have attempted to keep recommendations in agreement with the most current standards of care.

MULTIMEDIA

Section 10 of 11  

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• Follow-up
• Miscellaneous
• Multimedia
• References

Media file 1:  Snake envenomations, moccasins. Copperhead (Agkistrodon contortrix). Photo courtesy of George Bush.
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Media file 2:  Snake envenomations, moccasins. Cottonmouth or water moccasin (Agkistrodon piscivorus). Photo courtesy of Sean Bush, MD.
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Media file 3:  Snake envenomations, moccasins. Copperhead (Agkistrodon contortrix). Photo courtesy of Sean Bush, MD.
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Media file 4:  Wound measurement in snakebites. Courtesy of Carolinas Poison Center.
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Media type:  Image

REFERENCES

Section 11 of 11

• Authors and Editors
• Introduction
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• Differentials
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• Medication
• Follow-up
• Miscellaneous
• Multimedia
• References

• Burch JM, Agarwal R, Mattox KL, et al. The treatment of crotalid envenomation without antivenin. J Trauma. Jan 1988;28(1):35-43. [Medline].
• Bush SP, Thomas TL, et al. Envenomations in children. Pediatr Emerg Med Rep. 1997;2:1-12.
• Bush SP, Hegewald KG, Green SM, et al. Effects of a negative pressure venom extraction device (Extractor) on local tissue injury after artificial rattlesnake envenomation in a porcine model. Wilderness Environ Med. Fall 2000;11(3):180-8. [Medline].
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Article Last Updated: Jan 4, 2007