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Emergency Medicine > ENVIRONMENTAL
Lizard Envenomation
Article Last Updated: Jan 4, 2007
AUTHOR AND EDITOR INFORMATION
Section 1 of 11  
Author: Robert Norris, MD, Chief, Associate Professor, Department of Surgery, Division of Emergency Medicine, Stanford University Medical Center
Robert Norris is a member of the following medical societies: American College of Emergency Physicians, American Medical Association, California Medical Association, and Wilderness Medical Society
Editors: Mark S Slabinski, MD, FACEP, FAAEM, Vice President, EMP Medical Group; John T VanDeVoort, PharmD, ABAT, Director of Pharmacy, Sacred Heart Hospital; A Antoine Kazzi, MD, Chief of Service, Department of Emergency Medicine, Medical Director of the Emergency Unit, American University of Beirut; John D Halamka, MD, MS, Associate Professor of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center; Chief Information Officer, CareGroup Healthcare System and Harvard Medical School; Attending Physician, Division of Emergency Medicine, Beth Israel Deaconess Medical Center; Jonathan Adler, MD, Attending Physician, Department of Emergency Medicine, Massachusetts General Hospital; Division of Emergency Medicine, Harvard Medical School
Author and Editor Disclosure
Synonyms and related keywords:
lizard envenomations, venomous lizards, Gila monster, Heloderma suspectum, Mexican beaded lizard, Heloderma horridum
Background
Two species of venomous lizards exist, the Gila monster (Heloderma suspectum, with 2 subspecies) and the Mexican beaded lizard (Heloderma horridum, with 3 subspecies).
The Gila monster is found in the desert regions of Arizona, western New Mexico, southeastern California, the southern tip of Nevada, extreme southwestern Utah, and northwestern Mexico. The beaded lizard is found only in Mexico, south of the location range of the Gila monster.
Both lizards have heavy bodies with large heads and powerful jaws. The beaded lizard is larger than the Gila monster, reaching almost a meter in length, whereas the Gila monster's maximal size is approximately 0.5 m.
Pathophysiology
The venom apparatus is much less sophisticated than that of most venomous snakes. A pair of multilobed labial venom glands (modified submandibular glands) lie in the anterior portion of the lower jaw. Venom is conducted from each lobe through a duct and is deposited into a labial mucosal pocket adjacent to the anterior teeth.
The teeth (approximately 20 per jaw) are grooved and loosely attached to the jaws. Venom is conducted via capillary action along these grooves into the victim's tissues as the lizard bites and chews. The more irritated the lizard is when it bites, the more it salivates and the greater the venom yield. Effective envenomation in humans probably occurs in less than 70% of bites.
The venoms of these 2 lizards are remarkably similar and contain a number of components, including L-amino acid oxidase, hyaluronidase, phospholipase A, serotonin, and highly active kallikreins that release vasoactive kinins. The venom contains no neurotoxins or any enzymes that significantly affect coagulation. In laboratory animals, the venom is as potent as some rattlesnake venoms. Rare hypersensitivity to helodermatid venom has been reported.
Frequency
United States
Bites are very infrequent and usually involve captive specimens. A significant number of bites probably go unreported because private keepers of these protected lizards may be reluctant to seek medical attention.
International
No data regarding current incidence of bites by venomous lizards in Mexico are available.
Mortality/Morbidity
- No documented deaths caused solely by a Gila monster bite have occurred in the United States.
- It is believed that a prolonged bite to a small individual, such as an infant or toddler, could result in death.
- Severe pain following a helodermatid bite may last many hours and generalized weakness can persist for several days.
History
- The vast majority of individuals who are bitten by Gila monsters or beaded lizards are intentionally interacting with the animals, and the history of the bite usually is clear.
- To help estimate the severity of envenomation, it is important to estimate the length of time the lizard remained attached to the victim. While an effective envenomation can occur with a contact time of a few seconds, if the lizard manages to hang on for a period of minutes, the bite could be very serious, potentially lethal.
- The victim may present with many signs and symptoms, including the following:
- Multiple lacerations that may bleed profusely
- Severe throbbing or burning pain at the bite site that may radiate proximally
- Discoloration at the bite site (eg, cyanosis, ecchymosis)
- Generalized weakness
- Nausea and vomiting
- Shortness of breath
- Sweating
- Numbness
- Dizziness
- Faintness
- Progressive edema
- Painful lymph nodes
- Angioedema
Physical
Vital signs should be assessed and closely monitored.
- Local signs
- Multiple bleeding lacerations
- Edema
- Cyanosis or ecchymosis
- Vasospasm
- Retained teeth (Closely examine wounds and probe for foreign bodies.)
- Necrosis (rare)
- Systemic signs
- Tachycardia
- Hypotension
- Respiratory distress
- Diaphoresis
- Lymphangitis and lymphadenopathy
Snake Envenomations, Coral
Snake Envenomations, Mohave Rattle
Snake Envenomations, Rattle
Lab Studies
- Complete blood count
- The most common finding is an elevation in the WBC count.
- In rare severe cases, a drop in the platelet count may occur.
- Measure serum electrolyte levels, particularly if there is a history of significant underlying disease.
- Coagulation studies
- Helodermatid venoms do not appear to have any anticoagulant fractions. However, very rarely, reports of abnormal coagulation studies with severe bites have been documented. These rare coagulopathies are likely secondary to hemostatic changes occurring as a result of severe endothelial cell damage.
- It is reasonable to obtain a prothrombin time, an activated partial thromboplastin time, a fibrinogen level, and a measure of fibrin degradation products.
- Perform a urinalysis and look for any evidence of blood or casts.
- A cardiac panel, including a CK-MB, myoglobin, and troponin should be obtained if the victim has evidence of hemodynamic instability, chest pain, or an abnormal ECG result.
Imaging Studies
- Soft tissue radiographs may be obtained to look for retained teeth, although the sensitivity of such studies is low.
Other Tests
- Electrocardiogram
- Obtaining an ECG is reasonable because several reports of transient abnormalities have been reported in the literature.
- T-wave abnormalities, conduction disturbances, and 2 cases of acute myocardial infarction (one in a young patient without chest pain who had a possible history of cocaine use but no other cardiac risk factors) have been reported.
Prehospital Care
No evidence-based recommendations have been determined for field management of lizard envenomation.
- If the lizard remains attached to the victim, it immediately should be removed by any of a number of methods, such as prying the jaws apart with a stick or metal object, holding a flame under the animal's chin, or submerging the lizard in cold water. Care should be exercised to prevent additional bites to the victim or rescuer as the lizard will be enraged.
- If possible, the wound should be washed quickly with running water. Place a dressing on the wound to control any active bleeding, and apply a splint to limit movement of the extremity. The limb can be kept at approximately heart level during transport to medical care.
- No evidence to recommend the use of constrictive bands, compressive dressings, or suction is available.
- Do not make any incisions into the already damaged tissues.
- Although ice has been used to reduce pain, it can exacerbate local vasospasm.
- Victims showing evidence of shock should be kept in a supine position with legs elevated. If oxygen and intravenous fluids are available, these should be administered during transport to the hospital.
Emergency Department Care
- Closely monitor vital signs.
- Immediately begin cardiac and pulse oximetry monitoring.
- Establish 2 IV lines with isotonic sodium chloride solution.
- If hypotension occurs, begin brisk crystalloid resuscitation. If vital signs fail to improve with adequate saline infusion (eg, 20-40 mL/kg), albumin can be administered. Vasopressor agents rarely are necessary, but they may be beneficial in refractory cases.
- Wound care
- Clean the wounds with soap and water, and evaluate them for retained foreign bodies.
- A local anesthetic, such as lidocaine (without epinephrine), can be injected at the bite site to aid in pain control and to assist in exploration of the wounds for retained teeth or damage to underlying structures. Regional nerve blocks and judicious use of narcotics can be helpful in controlling pain. A non–histamine-releasing narcotic, such as fentanyl, may be preferable.
- The extremity should be splinted and kept at (or slightly above) the patient's heart level to reduce edema.
- Because of the significant local tissue trauma, prophylactic broad-spectrum antibiotics may be administered for a few days, although this treatment is controversial.
- Tetanus immunization status should be updated as necessary.
Consultations
Consult an expert in reptile envenomations to assist in management, as necessary. An excellent resource for assistance is the University of Arizona Poison and Drug Information Center (phone: 520/626-6016).
No specific agents are used to treat lizard envenomations. Although 2 experimental antivenoms have been produced for the Gila monster, neither has been made commercially available. Drug therapy is entirely symptomatic (eg, local anesthetics, analgesics, antiemetics). If antibiotics are administered, they should be broad-spectrum and they should provide coverage for gram-negative organisms. For the rare case of anaphylaxis/angioedema, therapy should be instituted with sympathomimetic agents, antihistamines, and/or steroids.
Drug Category: Cardiovascular Agents
Possess alpha- and beta-adrenergic effects that are useful in reversing anaphylactic reactions (eg, angioedema, bronchospasm, hypotension).
| Drug Name | Epinephrine (Adrenalin, EpiPen) |
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| Description | DOC for the treatment of anaphylactoid reactions. Alpha-agonist effects increase peripheral vascular resistance and reverse peripheral vasodilatation and vascular permeability, thus helping to restore vascular tone and blood pressure. The beta-agonist effects increase heart rate and inotropism and cause bronchodilatation |
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| Adult Dose | Initial dose is 0.01 mL/kg IM/SC of a 1:1000 solution; not to exceed 0.5 mL
In extreme anaphylactic states (eg, airway edema, shock, severe bronchospasm), give 10 mL of a 1:100,000 dilution of aqueous epinephrine IV over 10 min; if required, a continuous infusion can be utilized thereafter, starting at 1 mcg/min IV up to 4 mcg/min |
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| Pediatric Dose | Infuse 0.1 mcg/kg/min IV with increasing increments of 0.1 mcg/kg/min; not to exceed 1.5 mcg/kg/min |
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| Contraindications | Documented hypersensitivity; cardiac arrhythmias or angle-closure glaucoma; local anesthesia in areas such as fingers or toes because vasoconstriction may produce sloughing of tissue; do not use during labor (may delay second stage of labor) |
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| Interactions | Increases toxicity of beta- and alpha-blocking agents and that of halogenated inhalational anesthetics |
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| Pregnancy | C - Safety for use during pregnancy has not been established.
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| Precautions | Caution in elderly patients and persons with diabetes mellitus; caution in prostatic hypertrophy, hypertension, cardiovascular disease, hyperthyroidism, and cerebrovascular insufficiency; rapid IV infusions may cause death from cerebrovascular hemorrhage or cardiac arrhythmias |
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Drug Category: Corticosteroids
Onset of action is approximately 4-6 h, although some synergistic activity may be noted when simultaneously used with sympathomimetic agents. Steroids may be needed in the rare event of an allergic reaction to lizard venom. Corticosteroids have no role in the management of envenomation itself.
| Drug Name | Methylprednisolone (Solu-Medrol) |
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| Description | Decreases inflammation by suppressing the migration of polymorphonuclear leukocytes and reversing increased capillary permeability |
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| Adult Dose | 125-250 mg IV loading dose; followed by 0.5-1 mg/kg IV dose q6h for up to 5 d |
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| Pediatric Dose | 2 mg/kg IV loading dose; followed by 0.5-1.0 mg/kg IV dose q6h for up to 5 d |
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| Contraindications | Documented hypersensitivity; viral, fungal, or tubercular skin infections |
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| Interactions | Coadministration with digoxin may increase digitalis toxicity secondary to hypokalemia; estrogens may increase levels; phenobarbital, phenytoin, and rifampin may decrease levels (adjust dose); monitor patients for hypokalemia when taking medication concurrently with diuretics |
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| Pregnancy | C - Safety for use during pregnancy has not been established.
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| Precautions | Hyperglycemia, edema, osteonecrosis, peptic ulcer disease, hypokalemia, osteoporosis, euphoria, psychosis, growth suppression, myopathy, and infections are possible complications of glucocorticoid use |
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| Drug Name | Prednisone (Deltasone, Orasone, Meticorten) |
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| Description | Decreases inflammation by suppressing migration of polymorphonuclear leukocytes and reversing increased capillary permeability. |
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| Adult Dose | 1-2 mg/kg PO qd or divided bid until symptom resolution; followed by a 1-wk taper |
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| Pediatric Dose | Administer as in adults |
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| Contraindications | Documented hypersensitivity; viral, fungal, or tubercular infections |
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| Interactions | Coadministration with estrogens may decrease clearance; concurrent use with digoxin, may cause digitalis toxicity secondary to hypokalemia; phenobarbital, phenytoin, and rifampin may increase metabolism of glucocorticoids (consider increasing maintenance dose); monitor for hypokalemia with coadministration of diuretics |
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| Pregnancy | C - Safety for use during pregnancy has not been established.
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| Precautions | Abrupt discontinuation of glucocorticoids may cause adrenal crisis; hyperglycemia, edema, osteonecrosis, myopathy, peptic ulcer disease, hypokalemia, osteoporosis, euphoria, psychosis, myasthenia gravis, growth suppression, and infections may occur with glucocorticoid use |
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Drug Category: Antihistamines
Prevent the histamine response in sensory nerve endings and blood vessels. More effective in preventing histamine response than in reversing it.
| Drug Name | Cimetidine (Tagamet) |
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| Description | An H2 antagonist that, when combined with an H1 type, may be useful in treating itching and flushing in anaphylaxis, pruritus, urticaria, and contact dermatitis that do not respond to H1-receptor antagonists alone. Use in addition to H1 antihistamines. |
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| Adult Dose | Patients with persistent symptoms: 300 mg IV followed by PO administration as outpatient q6h for 2 d or for as long as clinically indicated |
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| Pediatric Dose | 25-30 mg/kg/d IV in 6 divided doses |
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| Contraindications | Documented hypersensitivity |
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| Interactions | Can increase blood levels of theophylline, warfarin, tricyclic antidepressants, triamterene, phenytoin, quinidine, propranolol, metronidazole, procainamide, and lidocaine |
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| Pregnancy | B - Usually safe but benefits must outweigh the risks.
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| Precautions | Elderly persons may experience confusional states; may cause impotence and gynecomastia in young males; may increase levels of many drugs; adjust dose or discontinue treatment if changes in renal function occur |
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| Drug Name | Diphenhydramine (Benadryl, Benylin, Bydramine) |
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| Description | Used for the symptomatic relief of allergic symptoms caused by histamine released in response to allergens. |
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| Adult Dose | 25-50 mg PO q6-8h prn; not to exceed 400 mg/d
10-50 mg IV/IM q6-8h prn; not to exceed 400 mg/d |
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| Pediatric Dose | 12.5-25 mg PO tid/qid or 5 mg/kg/d or 150 mg/m2/d divided tid/qid; not to exceed 300 mg/d
5 mg/kg/d or 150 mg/m2/d IV/IM divided qid; not to exceed 300 mg/d |
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| Contraindications | Documented hypersensitivity |
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| Interactions | Potentiates effect of CNS depressants; because of alcohol content, do not give syrup dosage form to patients taking medications that can cause disulfiramlike reactions |
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| Pregnancy | B - Usually safe but benefits must outweigh the risks.
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| Precautions | May exacerbate angle-closure glaucoma, hyperthyroidism, peptic ulcer, and urinary tract obstruction |
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Drug Category: Local anesthetics
Local anesthetics can be injected, either locally or regionally, to aid in exploration of wounds (to rule out damage to underlying structures or retained teeth).
| Drug Name | Lidocaine (Xylocaine) |
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| Description | Amide local anesthetic used in 1-2% concentration. Inhibits depolarization of type C sensory neurons by blocking sodium channels. Epinephrine should be avoided in venomous lizard bites to prevent causing additional local tissue ischemia. |
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| Adult Dose | 4.5 mg/kg topically, not to exceed 300 mg |
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| Pediatric Dose | Administer as in adults |
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| Contraindications | Documented hypersensitivity to amide-type local anesthetics; avoid in Adams-Stokes syndrome and Wolff-Parkinson-White syndrome; avoid in severe sinoatrial, atrioventricular (AV), or intraventricular block, if artificial pacemaker not in place |
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| Interactions | Coadministration with cimetidine or beta-blockers increases toxicity of lidocaine; coadministration with procainamide and tocainide may result in additive cardiodepressant action; may increase effects of succinylcholine |
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| Pregnancy | B - Usually safe but benefits must outweigh the risks.
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| Precautions | Use a solution without preservatives; caution in heart failure, hepatic disease, hypoxia, hypovolemia or shock, respiratory depression, and bradycardia; may increase risk of CNS and cardiac side effects in elderly persons; high plasma concentrations can cause seizures, heart block, and AV conduction abnormalities |
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Drug Category: Analgesics
Patients may require narcotic analgesics for pain control after venomous lizard bites. In choosing a narcotic analgesic, to prevent worsening venom effects, it is best to select a narcotic that has less tendency to induce histamine release, such as fentanyl.
| Drug Name | Fentanyl citrate (Sublimaze) |
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| Description | A synthetic opioid that is 75-200 times more potent and much shorter half-life than morphine sulfate. Has less hypotensive effects and is safer in patients with hyperactive airway disease than morphine because of minimal-to-no associated histamine release. By itself, it causes little cardiovascular compromise, although addition of benzodiazepines or other sedatives may result in decreased cardiac output and blood pressure.
Highly lipophilic and protein-bound. Prolonged exposure leads to accumulation in fat and delays weaning process.
Consider continuous infusion because of the short half-life of fentanyl. Parenteral form is DOC for conscious sedation analgesia. Ideal for analgesic action of short duration during anesthesia and immediate postoperative period.
Excellent choice for pain management and sedation with short duration (30-60 min) and easy to titrate. Easily and quickly reversed by naloxone.
After initial parenteral dose, subsequent parenteral doses should not be titrated more frequently than q3h or q6h thereafter.
Transdermal form is used only for chronic pain conditions in opioid-tolerant patients. When using transdermal dosage form, majority of patients are controlled with 72-h dosing intervals; however, some patients require dosing intervals of 48 h.
Easily and quickly reversed by naloxone. |
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| Adult Dose | Emergency: 0.5-2 mcg/kg/dose IM/IV
Analgesia: 0.5-1 mcg/kg/dose IM/IV q30-60min |
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| Pediatric Dose | <2 years: 2-3 mcg/kg/dose IM/IV q30-60min
2-12 years: 1-2 mcg/kg/dose IM/IV q60min
>12 years: Administer as in adults |
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| Contraindications | Documented hypersensitivity; hypotension or potentially compromised airway where it would be difficult to establish rapid airway control |
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| Interactions | Phenothiazines may antagonize analgesic effects of opiate agonists; tricyclic antidepressants may potentiate adverse effects of fentanyl when both drugs are used concurrently |
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| Pregnancy | C - Safety for use during pregnancy has not been established.
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| Precautions | Caution in hypotension, respiratory depression, constipation, nausea, emesis, and urinary retention; idiosyncratic reaction, known as chest wall rigidity syndrome, may require neuromuscular blockade in order to increase ventilation |
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Further Inpatient Care
- Admit patients with a significant systemic reaction or with abnormal lab study and/or ECG findings, possibly to a monitored setting.
- The bitten extremity should be placed in a well-padded splint and elevated to the patient's heart level or higher to reduce edema.
- Institute standard daily wound care, including cleansing, topical antibiotic application, and dressing.
- Physical therapy can help speed the return to full function.
- Admission for pain control may be warranted.
Further Outpatient Care
- All victims of helodermatid bites should be observed in the ED for at least 6 hours.
- If a reliable patient is relatively asymptomatic and all vital signs and lab findings are normal, discharge is appropriate if the patient is given instructions to return for any worsening symptoms.
- Provide instructions for wound care (eg, clean the wounds twice per day with soap and water, followed by peroxide; apply a topical antibiotic ointment and dressing).
- Signs and symptoms of wound infection should be discussed with the patient.
- Give a prescription for antibiotics (eg, cephalexin) to patients who are being prophylactically treated.
- A prescription for a narcotic analgesic, such as hydrocodone, may be appropriate.
- Arrange a follow-up appointment for a wound check in 24-48 hours.
Deterrence/Prevention
- Avoid handling or otherwise disturbing venomous lizards.
- Because these creatures spend approximately 99% of their lives underground, the opportunity to see one in the wild is a great privilege. The urge to pick up or capture it should be strongly suppressed. They are federally protected.
Complications
- Any of the attendant complications following shock may be encountered.
- Myocardial infarction may occur.
- Coagulopathy is a rare complication.
- Wound infections may occur, especially in the setting of a retained tooth.
- Necrosis is notably rare.
Prognosis
- The prognosis is excellent, although pain may be an issue for many days.
Patient Education
Medical/Legal Pitfalls
- Failure to fully evaluate a victim with a significant helodermatid bite potentially could lead to missing a rare coagulopathy or myocardial infarction.
- Much more likely is the possibility of missing a retained foreign body (eg, tooth) in the bite wound if the site is not examined carefully.
| Media file 1:
A Gila monster (Heloderma suspectum). Photo by Holly McNally. |
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| Media file 2:
Close-up of the head of a Gila monster. Clearly evident is the bulging musculature of the jaws, which gives this animal a tenacious bite. Photo by Holly McNally. |
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Media type: Photo
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| Media file 3:
The dentition of a Gila monster. The grooved surfaces of the teeth are evident. These grooves allow for venom movement from the venom glands into the victim's tissues. Photo by Michael Cardwell. |
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Media type: Photo
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| Media file 4:
A Gila monster (Heloderma suspectum). Photo by Michael Cardwell. |
 | View Full Size Image | |
Media type: Photo
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Lizard Envenomation excerpt Article Last Updated: Jan 4, 2007
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