AUTHOR AND EDITOR INFORMATION

Section 1 of 11  

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• Follow-up
• Miscellaneous
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INTRODUCTION

Section 2 of 11  

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Background

Rattlesnakes are pit vipers and include the genera Crotalus and Sistrurus. Pit vipers may be identified by a heat-sensing pit anteroinferior to the eye. Rattlesnakes may be identified in all but one species by a rattle at the tip of the tail. Rattlesnakes are indigenous from North America to South America.

Pathophysiology

Venom is usually injected into subcutaneous tissue via hollow movable fangs located in the anterior mouth. Occasionally, intramuscular or (probably rarely) intravenous injection occurs. Rattlesnake venom is generally composed of several digestive enzymes and spreading factors, which result in local and systemic injury.

Clinically, local effects most commonly predominate, progressing from pain and edema to ecchymosis and bullae. Hematologic abnormalities, including defibrination with or without thrombocytopenia, may result, but serious bleeding is uncommon. Local or diffuse myotoxicity may result in complications such as compartment syndrome or rhabdomyolysis. Other general effects include shock, myokymia/fasciculations, taste changes, and vomiting. Rarely, direct cardiotoxicity or allergy to venom may occur. Some rattlesnakes may exhibit neurotoxicity with minimal local tissue effects (see Snake Envenomations, Mohave Rattle).

Frequency

United States

Approximately 7,000-8,000 reptile bites are reported to the American Association of Poison Control Centers (AAPCC) each year. However, this figure is probably conservative because of underreporting. Rattlesnakes cause the majority of all bites by identified venomous snakes in the United States. Dry bite (ie, no clinical evidence of envenomation) occurs in between 10 and 50% of strikes.

International

An estimated 300,000-400,000 venomous snakebites occur per year. Although rattlesnakes are not found naturally outside of North America, Central America, and South America, they are imported into zoos, museums, and private collections in other regions of the world.

Mortality/Morbidity

Fewer than half a dozen deaths occur per year as a result of snakebite in the United States; most are caused by rattlesnake bites. Estimates of deaths each year from snakebite range from 30,000-110,000 worldwide. Up to 5 times as many individuals experience permanent morbidity.

US mortality with administration of antivenin is approximately 0.28%. Without antivenin being administered, mortality is approximately 2.6%.

Sex

Males are bitten more commonly than females.

Age

Young adults are bitten most commonly.

CLINICAL

Section 3 of 11  

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• Follow-up
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History

All or none of the following may be present. Note that symptoms are subject to change, and this change can be very rapid or very insidious. In addition, severity is generally guided by the most severely affected parameter.

• Pain around the bite site
• Swelling
• Taste changes (eg, a metallic taste)
• Difficulty breathing
• Chest pain
• Nausea, vomiting, or diarrhea
• Hematemesis, hematochezia
• Neurologic symptoms
• • Weakness
  • Paresthesias
• Syncope, near syncope

Physical

• Fang marks - May be 1, 2, or more, or may be unable to discern
• Tenderness surrounding the bite site
• Local edema
• • Use a pen to mark and time the border of advancing edema every 15-20 minutes initially. Once stabilization with antivenom has occurred, repeat measurements every 1-2 hours.
  • Rapidly progressive swelling is usually indicative of a severe envenomation.
• Erythema
• Ecchymosis
• Bullae
• Bleeding
• Hypotension/hypertension
• Tachycardia
• Myokymia (muscle fasciculations)
• Neurologic effects
• Lethargy

Causes

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

DIFFERENTIALS

Section 4 of 11  

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WORKUP

Section 5 of 11  

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Lab Studies

• Coagulopathy commonly occurs with rattlesnake envenomation, although clinical bleeding is uncommon. Defibrination and/or thrombocytopenia most often characterize snakebite coagulopathy. Defibrination is manifested by low serum fibrinogen, elevated prothrombin time, and elevated fibrin split products (FSP). Venom-induced thrombocytopenia may exist in association with or independently of defibrination. Abnormal coagulation parameters may last for a week or more. Recurrence of coagulopathy after resolution with antivenom has been reported.
• • Complete blood count (CBC) with differential
  • Platelets
  • Prothrombin time
  • Activated partial thromboplastin time
  • Fibrinogen
  • Type and screen
  • Urinalysis
• Rhabdomyolysis may occur from severe envenomation but is best described after canebrake (Crotalus horridus atricaudatus) and Mohave (Crotalus scutulatus) rattlesnake envenomations. Rhabdomyolysis may lead to myoglobinuric renal failure and subsequent electrolyte abnormalities, such as hyperkalemia, hypokalemia, or hypocalcemia.
• • Creatine kinase (CK)
  • Electrolytes
  • Blood urea nitrogen (BUN), creatinine
  • Calcium
  • Phosphorus
  • Urinalysis
• For respiratory difficulty, consider arterial blood gases (ABGs), although arterial puncture should be avoided if a severe venom-induced coagulopathy develops.
• Obtain laboratory and other diagnostic data on a case-by-case basis. Factors to consider may include severity of envenomation, physician preference, and cost.

Imaging Studies

• Plain radiographs may depict teeth or fangs retained in the wound.
• Consider a head CT if the patient has a headache or altered level of consciousness (ALOC) with a severe coagulopathy.

Other Tests

• Obtain an electrocardiogram (ECG), if indicated.
• Skin testing
• • Skin testing is not necessary before administering Crotaline Fab antivenom (CroFab) therapy. Skin testing is described below for educational purposes or for the unusual case in which a practitioner determines it is indicated.
  • Intracutaneous injection of 0.02-0.03 mL of a 1:10 dilution of horse serum or antivenom is recommended in the Antivenin (Crotalidae) Polyvalent package insert.
  • • A positive test result is manifested by the development of a wheal within 5-30 minutes.
    • However, skin testing is very unreliable. False-positive and false-negative test results may occur.
    • Using antivenom (further diluted to 1:100), rather than the horse serum control that is supplied, may increase the sensitivity and specificity of the test.
    • Skin testing may be considered useful in variably predicting immediate hypersensitivity in cases of moderate envenomation when it is uncertain whether the need for antivenom outweighs the risk of anaphylaxis.
    • Skin testing may sensitize individuals at risk for future exposures to antivenom, or it may precipitate anaphylaxis.
    • If antivenom is clearly indicated, it should be started as described below, without waiting to conduct a skin test.

Procedures

• Central venous or interosseous access may need to be obtained. However, avoid placing a central line in a noncompressible site (eg, internal jugular) because of the risk of bleeding from venom-induced coagulopathy.
• Fasciotomy may be indicated if measured compartment pressures remain persistently and severely elevated despite adequate antivenom. CroFab has been shown to limit the decrease in perfusion pressure associated with compartment syndrome.
• • Compartment syndrome may manifest subjectively, with complaints of increasing pain, and objectively, with tenderness on passive muscle stretch, a rock hard feel to the compartment or a diminished capillary refill.
  • True compartment syndrome is rare following snakebite, even in patients with severe edema, because most envenomations are believed to be subcutaneous.
  • Myonecrosis has been shown to occur from direct myotoxicity, even after fasciotomy of the affected compartment.
  • Distinguishing compartment syndrome from the effects of envenomation may be difficult. Similar to compartment syndrome, rattlesnake envenomation may cause a bluish discoloration of the skin or pallor (because of subcutaneous bruising), severe swelling, paresthesias, and pain. If effects are only caused by envenomation and the patient does not have compartment syndrome, capillary refill is normal and compartmental pressure is not elevated.

TREATMENT

Section 6 of 11  

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Prehospital Care

Do nothing to injure the patient or impede travel to the ED.

• Give general support of airway, breathing and circulation per advanced cardiac life support (ACLS) protocol with oxygen, monitors, 2 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. Use a pen to mark and time the border of advancing edema often enough to gauge progression.
• 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. Limiting venom spread actually may be deleterious for pit viper envenomation if it increases local necrosis or compartment pressure. Tourniquets are not recommended.
• Maintain the extremity in a neutral position.
• First aid techniques that lack therapeutic value or are potentially more harmful than the snakebite include electric shock, alcohol, stimulants, aspirin, placing ice on the wound, 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 cannot be recommended because of the risk of additional injury. If uncertainty exists about whether a particular snake is venomous, 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 two isotonic sodium chloride solution challenges (eg, 20 mL/kg). Treat persistent shock with colloids, followed by pressors as indicated.

• Administer antivenom for signs of envenomation progression or imminent risk of an acute complication of envenomation (see Complications). Because CroFab appears safer than Antivenin Crotalidae Polyvalent, it is indicated even if the envenomation is minimal or mild. It should be given as a preventative measure if any signs of envenomation exist. Do not wait for the envenomation to get worse—permanent injury could result.
• It is emphasized that grading envenomations is a dynamic process and additional antivenom should be given as indicated by a worsening clinical course. When considering the use of antivenom, the risk of adverse reaction to antivenom must be weighed against the benefits of reducing venom toxicity. Alternatives (eg, a different type of antivenom, if available) should be considered as well.
• Nonenvenomation, ie, dry bite (probably occurs in <10% of rattlesnake bites, although estimates as high as 50% exist)
• • 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 part
  • Systemic effects - Present but not life threatening; may include nausea, vomiting, oral paresthesias or unusual tastes, fasciculations (myokymia), mild hypotension (systolic blood pressure <90 mm Hg), mild tachycardia (heart rate <150 bpm), and tachypnea
  • Coagulation abnormalities - Laboratory evidence of coagulation abnormalities may be present, but no clinical evidence of abnormal bleeding or clotting exists; rattlesnake venom-induced coagulopathies commonly include thrombocytopenia, decreased fibrinogen, and/or elevated PT
• Severe envenomation
• • Local effects - Swelling, pain, tenderness, and/or ecchymosis extending beyond the entire extremity or threatening the airway
  • Systemic effects - May include severe hypotension or shock, severe tachycardia or tachypnea, respiratory insufficiency, and/or severe altered mental status
  • Coagulation abnormalities - Markedly abnormal with serious bleeding or severe threat of bleeding

Consultations

• The American Association of Poison Control Centers may assist in the management of envenomations.
• For assistance regarding use of CroFab for a patient bitten by a snake, contact the CroFab hotline at 1-87-SERPDRUG (1-877-377-3784).
• Consider consulting a surgeon (eg, general, orthopedic, hand) if compartment syndrome is suspected.

MEDICATION

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The only proven therapy for snakebites is antivenom. The physician also must be prepared to support the victim's cardiovascular and respiratory systems.

Drug Category: Antivenom

This agent neutralizes toxins from snakebites. Two antivenoms are available: CroFab and Antivenin Crotalidae Polyvalent. CroFab has been available since December 2000. CroFab is manufactured by Protherics Inc, Nashville, Tennessee and distributed by Fougera, Melville, New York (800-231-0206). Antivenin Crotalidae Polyvalent, manufactured by Wyeth-Ayerst, is still available on the shelves of many hospital pharmacies but is no longer being produced. Whether the production of Antivenin will resume is unknown. Meanwhile, another antivenom (Antivipmyn, manufactured by Instituto Bioclon S.A. de C.V.) has been FDA approved for experimental use and is currently undergoing phase III clinical trials.

Drug Category: Antihistamines

These agents are used for treatment of acute allergic reactions to antivenom or venom (not for treatment of envenomation).

Drug Category: Immunizations

Patients should be immunized against tetanus.

Drug Category: Antibiotics

Prophylactic antibiotics are not routinely indicated. However, wound infections should be treated with antibiotics. Common etiologic bacteria in wound infections include Pseudomonas aeruginosa, Staphylococcus epidermidis, Enterobacteriaceae species, and Clostridium species. For infected wounds, empiric therapy may include ciprofloxacin (contraindicated in pediatric patients and pregnant women) as a single agent or a combination of ceftriaxone plus amoxicillin-clavulanate, pending wound culture and sensitivity results. Retained foreign bodies (eg, a fang, other tooth) are a common cause of wound infection.

Drug Category: Analgesics

Pain control is essential to quality patient care. It ensures patient comfort and promotes pulmonary toilet. Most analgesics have sedating properties, which are beneficial for patients who have sustained painful snakebites. Opioid analgesics are recommended for pain control as needed. NSAIDs may contribute to coagulopathies.

Drug Category: Hematologic Agents

Consider transfusion if antivenom does not correct coagulopathy or if imminent risk of serious bleeding. Transfusion is generally recommended for life-threatening bleeding (rare), platelets <20,000 mm³, or hemoglobin <7 g/dL. Transfusion should be utilized after antivenom as a temporizing or adjuvant measure because antivenom may correct coagulopathies more definitively (although this is an area with particularly contradictory literature). Coagulopathy often recurs and may persist for 2 weeks or more after envenomation.

FOLLOW-UP

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Further Inpatient Care

• All patients with rattlesnake envenomation should be admitted to the hospital and remain there while undergoing treatment with antivenom. Close observation and frequent measurements of swelling (every 1-2 h) for approximately 24 hours after initial control is recommended.
• Patients who are believed to have a dry bite in which no venom effects develop should be observed for at least 8 hours. A close follow-up and/or recheck examination is recommended.
• 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.

Further Outpatient Care

• Discharge instructions should include the following:
• • Return immediately if swelling worsens or pain becomes severe.
  • Return immediately if any abnormal bleeding or bruising, petechiae, dark tarry stools, or severe headache occur.
  • Return for signs of wound infection, such as swelling, excessive tenderness, redness or streaks, heat, or drainage (pus).
  • 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. If bitten on the foot or leg, crutches and crutch training should be provided. Elevate and mobilize affected extremity as tolerated.
  • Next day wound check should be performed at the physician's discretion on a case-by-case basis. The patient should return to the ED or follow up every 3 days for 2 weeks with repeat CBC, PT/INR, and fibrinogen. Laboratory results may need to be rechecked more or less frequently or for a longer or shorter duration on a case-by-case basis.

In/Out Patient Meds

• Administer antihistamines if serum sickness develops. Steroids may be indicated for more severe cases of serum sickness.

Transfer

• All hospitals should have enough antivenom to treat at least one patient. However, antidote stocking varies and shortages do occur. Therefore, if antivenom is not available at the presenting hospital, the patient should be transferred to a facility where antivenom may be administered. However, if it is available, antivenom may be necessary to optimize stabilization of a patient prior to transfer.

Deterrence/Prevention

• Never handle a rattlesnake, even if it is believed to be dead. Serious, even fatal, envenomations have been documented to occur after handling the decapitated head of a rattlesnake up to 90 minutes after it was severed.
• 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 in indigenous areas.
• Keep the garage door closed to prevent rattlesnakes from seeking shelter in the garage.
• Many cases of envenomation involve alcohol. Do not use alcohol and place oneself in an environment that may be shared with rattlesnakes or play with snakes while intoxicated.

Complications

• Bleeding, such as gastrointestinal or intracranial
• Compartment syndrome
• Necrosis with resulting tissue loss or loss of function
• Rhabdomyolysis, myoglobinuric renal failure
• Infection
• Respiratory difficulty
• Death (rare in the United States)
• Antivenom-associated complications
• • Anaphylaxis is a type I (immediate) hypersensitivity reaction, which may be life threatening. It is characterized by urticaria, airway swelling, wheezing, and shock. Some degree of anaphylaxis may occur in as many as 25% of patients given Antivenin (Crotalidae) Polyvalent. Risk factors include previous exposure to horse serum or antivenom or a history of reactive airways. Immediate hypersensitivity is treated with epinephrine, antihistamines, steroids, and ventilatory/circulatory support, as needed. Although experience is limited, immediate hypersensitivity is less common after treatment with CroFab.
  • Serum sickness is a type III (delayed) hypersensitivity reaction. It is characterized by fever, urticaria, lymphadenopathy, and arthritis and may occur 3 days to 3 weeks after Antivenin (Crotalidae) Polyvalent administration in as many as 50% of patients. Serum sickness is dose-related; it almost always occurs when more than 8 vials of Antivenin (Crotalidae) Polyvalent are administered. Although serum sickness can be uncomfortable, it is usually benign and self-limited and is treated with steroids and antihistamines. Delayed hypersensitivity is much less common after treatment with CroFab, although experience with this relatively new medication is limited.

Prognosis

• Before antivenom, estimates of mortality rates ranged from 5-25%.
• • Since the development of antivenom, rapid EMS transport, and emergency/intensive care, mortality rates have improved to less than 0.28% when antivenom is administered and to 2.6% when antivenom is not administered.
  • Less specific figures are available for morbidity data, although most patients recover fully after rattlesnake envenomation. The best estimates suggest that rattlesnake envenomation results in tissue loss, deformity, or loss of function in approximately 10% of patients.

Patient Education

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

MISCELLANEOUS

Section 9 of 11  

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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.
• 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 rattlesnake 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. Although controversy exists, the authors have attempted to keep recommendations in agreement with the most current standards of care.
• These are guidelines, and the clinician should use judgment for individual patient encounters.

MULTIMEDIA

Section 10 of 11  

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• Multimedia
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Media file 1:  Juvenile southern Pacific rattlesnake (Crotalus oreganus helleri). Photo by Sean Bush, MD.
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Media file 2:  A recent study suggests that the Extractor (Sawyer Products) does not reduce swelling after rattlesnake envenomation and may be associated with skin necrosis beneath the suction cup. Photo by Sean Bush, MD.
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Media type:  Photo

Media file 3:  Moderate rattlesnake envenomation in a toddler after treatment with antivenom. Photo by Sean Bush, MD.
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REFERENCES

Section 11 of 11

• Authors and Editors
• Introduction
• Clinical
• Differentials
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• Miscellaneous
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• References

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• Bond RG, Burkhart KK. Thrombocytopenia following timber rattlesnake envenomation. Ann Emerg Med. Jul 1997;30(1):40-4. [Medline].
• Boyer LV, Seifert SA, Clark RF, McNally JT, Williams SR, Nordt SP, et al. Recurrent and persistent coagulopathy following pit viper envenomation. Arch Intern Med. Apr 12 1999;159(7):706-10. [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].
• Burgess JL, Dart RC. Snake venom coagulopathy: use and abuse of blood products in the treatment of pit viper envenomation. Ann Emerg Med. Jul 1991;20(7):795-801. [Medline].
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• Langley RL, Morrow WE. Deaths resulting from animal attacks in the United States. Wilderness Environ Med. 1997;8:8-16.
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• Norris RL Jr. Snake Venom Poisoning in the United States: Assessment and Management. Emerg Med Rep. 1995;16:87-94.
• Offerman SR, Bush SP, Moynihan JA, Clark RF. Crotaline Fab antivenom for the treatment of children with rattlesnake envenomation. Pediatrics. Nov 2002;110(5):968-71. [Medline].
• Premawardhena AP, de Silva CE, Fonseka MM, Gunatilake SB, de Silva HJ. Low dose subcutaneous adrenaline to prevent acute adverse reactions to antivenom serum in people bitten by snakes: randomised, placebo controlled trial. BMJ. Apr 17 1999;318(7190):1041-3. [Medline].
• Riffer E, Curry SC, Gerkin R. Successful treatment with antivenin of marked thrombocytopenia without significant coagulopathy following rattlesnake bite. Ann Emerg Med. Nov 1987;16(11):1297-9. [Medline].
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Article Last Updated: Jul 24, 2008