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Scorpion Envenomation: Treatment & Medication

Author: David Cheng, MD, Assistant Professor of Emergency Medicine, Associate Emergency Medicine Residency Director, Associate Medical Director of Emergency Services, University of Arkansas Medical Sciences
Coauthor(s): Judith A Dattaro, MD, FACEP, Assistant Professor of Emergency Medicine in Surgery, Cornell University Medical College; Consulting Staff, Department of Emergency Medicine, Weill-Cornell University Medical Center, New York Presbyterian Hospital; Ramy Yakobi, MD, MBA, Medical Director of Emergency Department, Beth Israel/Kings Highway Division; Lecturer, Physician Assistant School, Cornell School of Medicine; Lecturer, Pre-hospital Management of Patient, Cornell/New York Presbyterian Hospital; Director of Emergency Department, New York Community Hospital
Contributor Information and Disclosures

Updated: Aug 6, 2009

Treatment

Medical Care

Prehospital Care

• Primary assessment of airway, breathing, and circulation takes precedence.
• Few studies have evaluated the utility of most first aid.
• The utility of negative pressure extraction devices has not been evaluated for scorpion stings.
• Perform endotracheal intubation and vascular access as needed.

Emergency Department Care

Supportive care is the backbone of treatment for systemic symptomatology.

• Grades of Centruroides envenomation  
  • Grade I - Local pain and/or paresthesias at the site of envenomation
  • Grade II - Pain and/or paresthesias remote from the site of the sting, in addition to local findings
  • Grade III - Either cranial nerve/autonomic dysfunction or somatic skeletal neuromuscular dysfunction
    • Cranial nerve dysfunction - Blurred vision, roving eye movements, hypersalivation, tongue fasciculations, dysphagia, dysphonia, problems with upper airway
    • Somatic skeletal neuromuscular dysfunction - Restlessness, severe involuntary shaking or jerking of the extremities that may be mistaken for a seizure
  • Grade IV - Combined cranial nerve/autonomic dysfunction and somatic nerve dysfunction
• Androctonus australis Hector Hospitalization Score
  • Priapism: +3                               
  • Vomiting: +2                               
  • SBP >160: +2                              
  • Corticosteroid PTA: +2             
  • Temperature >38ºC: +1              
  • Heart rate >100 bpm: +1            

Total >2 = Hospitalization

• Although grading and scoring systems have been developed they are limited due to species specificity and low degree a symptoms that would lead to hospitalization or therapy.

Medical care

Because the clinical manifestations and severity of the symptoms vary among patients, individualize management of scorpion stings. Furthermore, frequent patient monitoring allows earlier recognition of the life-threatening problems of scorpion envenomation. Treatment generally consists of moving the patient away from the scorpion and stabilizing the patient's airway and vital signs, followed by administration of antivenin and institution of symptomatic and local treatment.

• Local treatment is discussed as follows:
  • A negative-pressure extraction device (ie, the extractor) may be useful, although the benefit is unproven. The extractor creates a negative pressure of 1 atm. Apply it to the sting site after incision. Oral extraction is contraindicated.
  • Use ice bags to reduce pain and to slow the absorption of venom via vasoconstriction. This is most effective during the first 2 hours following the sting.
  • Immobilize the affected part in a functional position below the level of the heart to delay venom absorption.
  • Calm the patient to lower the heart rate and blood pressure, thus limiting the spread of the venom.
  • For medical delay secondary to remoteness, consider applying a lymphatic-venous compression wrap 1 inch proximal to the sting site to reduce superficial venous and lymphatic flow of the venom but not to stop the arterial flow. Only remove this wrap when the provider is ready to administer systemic support. The drawback of this wrap is that it may intensify the local effects of the venom.
  • Apply a topical or local anesthetic agent to the wound to decrease paresthesia; this tends to be more effective than opiates.
  • Administer local wound care and topical antibiotic to the wound.
  • Administer tetanus prophylaxis.
  • Administer systemic antibiotics if signs of secondary infection occur.
  • Administer muscle relaxants for severe muscle spasms (ie, benzodiazepines.)
• Systemic treatment is instituted by directing supportive care toward the organ specifically affected by the venom.
  • Establish airway, breathing, and circulation (ie, ABCs) to provide adequate airway, ventilation, and perfusion.
  • Monitor vital signs (eg, pulse oximetry; heart rate, blood pressure, and respiratory rate monitor).
  • Use invasive monitoring for patients who are unstable and hemodynamic.
  • Administer oxygen.
  • Administer intravenous fluids to help prevent hypovolemia from vomiting, diarrhea, sweating, hypersalivation, and insensible water loss from a tropical environment.
  • Perform intubation and institute mechanical ventilation with end-tidal carbon dioxide monitoring for patients in respiratory distress.
  • For hyperdynamic cardiovascular changes, administration of a combination of beta-blockers with sympathetic alpha-blockers is most effective in reversing this venom-induced effect. Avoid using beta-blockers alone because this leads to an unopposed alpha-adrenergic effect. Also, nitrates can be used for hypertension and myocardial ischemia.
  • For hypodynamic cardiac changes, a titrated monitored fluid infusion with afterload reduction helps reduce mortality. A diuretic may be used for pulmonary edema in the absence of hypovolemia, but an afterload reducer, such as prazosin, nifedipine, nitroprusside, hydralazine, or angiotensin-converting enzyme inhibitors, is better. Inotropic medications, such as digitalis, have little effect, while dopamine aggravates the myocardial damage through catecholaminelike actions. Dobutamine seems to be a better choice for the inotropic effect. Finally, a pressor such as norepinephrine can be used as a last resort to correct hypotension refractory to fluid therapy.
  • Administer atropine to counter venom-induced parasympathomimetic effects.
• Insulin administration in scorpion envenomation animal experiments has helped the vital organs to use metabolic substrates more efficiently, thus preventing venom-induced multiorgan failure, especially cardiopulmonary failure. Unfortunately, no human studies have been conducted.
• Administer barbiturates and/or a benzodiazepine continuous infusion for severe excessive motor activity.
• The use of steroids to decrease shock and edema is of unproven benefit.
• Antivenin is the treatment of choice after supportive care is established. The quantity to be used is determined by the clinical severity of patients and by their evolution over time. Unfortunately, predicting the evolution of symptoms and, thus, the amount of antivenin that is needed in the future, is difficult.
  • The antivenin significantly decreases the level of circulating unbound venom within an hour. The persistence of symptoms after the administration of antivenin is due to the inability of the antivenin to neutralize scorpion toxins already bound to their target receptors.
  • Time guidelines for the disappearance of symptoms after antivenin administration are as follows:
    • Centruroides antivenin: Severe neurologic symptoms reverse in 15-30 min. Mild-to-moderate neurologic symptoms reverse in 45-90 min.
    • Non-Centruroides antivenin: In the first hour, local pain abates. In 6-12 hours, agitation, sweating, and hyperglycemia abate. In 6-24 hours, cardiorespiratory symptoms abate.
  • While an anaphylaxis reaction to the antivenin is possible, the patient is at lower risk for this than with other antivenins for other poisonous envenomations because of the huge release of catecholamines induced by the scorpion venom. However, the larger the dose of antivenin, the greater the chance for serum sickness.
  • In a prospective, randomized, double-blind study, Boyer et al compared scorpion-specific F(ab')₂ antivenom (Anascorp, Centruroides [scorpion] immune F(ab)₂ intravenous [equine], Instituto Bioclon) (n=8) with placebo (n=7)  in children who developed neurotoxic symptoms following scorpion envenomation. Neuromotor abnormalities were present in all patients at baseline, and respiratory distress was present in 20%. Beginning 2 hours after treatment, symptom resolution differed significantly in the antivenom group compared with the placebo group. Plasma venom concentrations were undetectable and cessation of the neurologic syndrome occurred within 4 hours in 100% of antivenom recipients compared with 1 placebo recipient (p=0.001). In this study, scorpion-specific F(ab')₂ antivenom successfully treated the clinical syndrome, reducing the need for concomitant sedation and reducing circulatingunbound venom levels.⁶
• A vaccine preparation was tried in experimental animals but was not pursued because of the need to prepare different antigens according to different geographical areas and to different species of scorpions living in the same area.
• In some cases, be aware that meperidine and morphine may potentiate the venom. Also, the concurrent use of barbiturates and narcotics may add to the respiratory depression in patients who have been envenomated.

Consultations

Local poison control centers may assist in management of envenomations.

• Contact the American Association of Poison Control Centers (800-222-1222) to be connected to a local poison control center.
• The University of Arizona Poison and Drug Information Center (520-626-6016 from outside Arizona or 800-362-0101 from Arizona only) has special experience in Centruroides envenomation.
• The Antivenom Index, published jointly by the American Association of Poison Control Centers and the American Zoo and Aquarium Association, lists the locations, amounts, and various types of antivenom stores.

Activity

• Rest and immobilization of the sting site is recommended to prevent rapid absorption of the venom into the circulation.

Medication

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

Analgesia may be indicated. Exercise caution when using narcotics for a patient with an unsecured airway because respiratory depressive effects may be synergistic with some scorpion venoms. Some recommend against using narcotics to treat scorpion envenomation with signs of systemic toxicity, especially in children. Tetanus prophylaxis is recommended if the patient cannot verify current status. Prophylactic antibiotic therapy is not required. Corticosteroids have not been shown useful in treating venom toxicity. Hypertensive emergencies may require standard antihypertensive therapy. Conversely, hypotension may require fluid resuscitation and/or vasopressors.

Cardiovascular agents can be used to elevate or decrease blood pressure and increase heart rate. Vasopressors and inotropic agents may be necessary in patients who already have been adequately volume resuscitated but remain in shock. Conversely, antihypertensives may be needed in patients with sympathetic-induced hypertension. In particular, the use of the alpha-blocking agent prazosin has been used and recommended. However, all published evidence recommending for or against this agent has come from either retrospective observational or prospective cohort studies. A true randomized controlled trial of this agent has not been published. 

At this time, no clear evidence exists as to which agent is most beneficial in specific circumstances. Autonomic instability from scorpion envenomation may lead to rapid, dramatic fluctuations in heart rate and blood pressure. Although many agents have rapid onset, they may also have prolonged effects. Should a hypertensive patient receive a longer-acting agent they may still have medication effects if they develop subsequent hypotension. In any case, agents should be chosen with detailed knowledge of their pharmacology and understanding of the pathophysiology of scorpion venom described above. Ideally, the agents are effective, have rapid onset, can be titrated to effect, have a short half-life if discontinued, and have minimal side effects.

A total of 22 types of scorpion antivenom are listed in the American Zoo and Aquarium Association Antivenom Index. They are available for a number of different species and have varied efficacy. Antivenom use remains controversial. Many researchers report decreased morbidity, mortality, and hospital stay with its use. These researchers and clinicians believe that antivenom therapy cannot be matched by supportive care in severe Buthidae scorpion envenomation. Others suggest that adverse effects (eg, anaphylactic reactions, serum sickness) limit or contraindicate antivenom use.

Until recently, the antivenom for stings by the bark scorpion was manufactured in the Antivenin Production Laboratory of Arizona State University. Its use was controversial. It had been shown to produce rapid resolution of systemic symptoms but not to affect pain or paresthesias. Subsequently, many physicians recommended it in grade III and grade IV envenomations. Adverse effects included immediate and delayed hypersensitivity reactions. Initially, these reactions were rare, but they increased in frequency. This leads some physicians to prefer supportive care only, as they felt that the treatment was potentially worse than the disease. As death was rare if existent, they felt supportive care would yield similar outcomes. Currently, it is no longer being produced. Subsequently, an increased pediatric ICU admission rate of 500% is being reported with scorpion envenomation.

Antivenins

Scorpion toxins are not good antigens because of small size and poor immunogenicity. They do not induce antibodies that cross-react against toxins of other scorpion species unless a 95% amino acid sequence homology exists between the 2 toxins. Thus, no universal antivenin is available. Instead, 22 types of scorpion antivenin exist.

Furthermore, the neurotoxin component of the scorpion venom tends to be the least immunogenic, resulting in the low efficiency for neurological complications. It usually is prepared from horses because they yield larger quantities. Sheep, goat, or bovine antivenin may be prepared if patient sensitivity to horse serum occurs.

A recent idea was to mix a batch of different scorpion antivenin together to create a universal antivenin, but this exposes the patient to unnecessary antivenin from scorpion species not from the patient's region.

Perform a skin test prior to administering the antivenin. First, dilute 0.1 mL of antivenin in a 1:10 ratio with isotonic sodium chloride solution. Second, administer 0.2 mL intradermally. A positive test result is if a wheal develops within 10 minutes. The skin test has a sensitivity of 96% and a specificity of 68%.

The best result occurs when antivenin is administered as early as possible (preferably within the first 2 h after the sting) and with adequate quantities to neutralize the venom (usually 50-100 times the LD50 amount). A decrease in curative effects occurs with longer sting-serotherapy delay and administration of insufficient amounts of antivenin.

USA-APL Centruroides scorpion antivenin

Used to neutralize toxins from scorpions. Produced in Arizona (for use in Arizona only). Not approved by FDA. Use remains controversial, but many physicians recommend it in grade III and IV envenomations. Shown to produce rapid resolution of systemic symptoms but does not affect pain or paresthesias. Results in resolution of symptoms within min to 2 h after administration. Antivenin treatment is based on venom burden, not patient's size. The smaller the victim, the more important it is to administer the full dose because of the venom dose-dependent severity.

Antihistamines

Prevent the histamine response in sensory nerve endings and blood vessels. They are more effective in preventing histamine response than in reversing it.

Cimetidine (Tagamet)

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. Other H2 antagonists are also available.

Diphenhydramine (Benadryl, Benylin, Bydramine)

Used for the symptomatic relief of allergic symptoms caused by histamine released in response to allergens.

Toxoids

Wounds resulting from scorpion sting are at risk of Clostridium tetani infection. A booster injection in previously immunized individuals is recommended to prevent this potentially lethal syndrome. Administer tetanus immune globulin (Hyper-Tet) to patients not immunized against C tetani products (eg, persons who have immigrated, elderly individuals).

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

Immune globulins

These agents induce passive immunity. Administer to patients not immunized against C tetani products (eg, persons who have immigrated, elderly individuals).

Tetanus immune globulin (Hyper-Tet)

Used for passive immunization of any person with a wound that might be contaminated with tetanus spores.

Benzodiazepines

By increasing the action of GABA (inhibitory neurotransmitter), counteract scorpion-induced excessive motor activity and nervous system excitation.

Lorazepam (Ativan)

Sedative hypnotic with short onset of effects and relatively long half-life.
By increasing action of GABA, which is a major inhibitory neurotransmitter in the brain, may depress all levels of CNS, including limbic and reticular formation.

Midazolam (Versed)

Short-acting benzodiazepine that can be administered in continuous infusion for severe nervous system excitation.

Barbiturates

Used to counteract scorpion-induced hyperactivity.

Pentobarbital (Nembutal)

Short-acting barbiturate with sedative and anticonvulsant properties used to produce barbiturate coma for severe CNS hyperexcitation. Requires patient intubation prior to use.

Local anesthetics

Tend to be more effective than opiates to control paresthesia and pain at the sting site.

Bupivacaine (Marcaine)

May reduce pain by slowing nerve impulse propagation and reducing action potential, which, in turn, prevents initiation and conduction of nerve impulses.

Adrenergic blocking agents and vasodilators

Used to counteract the scorpion-induced adrenergic cardiovascular effect.

Labetalol (Normodyne, Trandate)

Blocks beta1-adrenergic, alpha-adrenergic, and beta2-adrenergic receptor sites, decreasing blood pressure.

Prazosin (Minipress)

Counteracts scorpion-induced adrenergic cardiovascular effects. May improve pulmonary edema through vasodilatory effects.

Hydralazine (Apresoline)

Decreases systemic resistance through direct vasodilation of arterioles

Anticholinergics

Used to counteract scorpion-induced cholinergic symptoms. Current recommendations are for use in treating symptomatic bradycardias. Traditionally, its use to dry venom-induced, excess, respiratory secretions has been warned against because of its potential adverse cardiopulmonary effects. It may exacerbate pulmonary edema and hypertension and may lead to a subsequent tachycardia. A recent case series has suggested relative efficacy and safety with its use in 5 pediatric patients treated for C sculpturatus sting. However, this should be considered an area in need of further study rather than a change in recommendations.

Atropine (Atropair)

Used to increase heart rate through vagolytic effects, causing an increase in cardiac output. Also treats bronchorrhea associated with scorpion envenomations. Atropine causes a reversible blockade of muscarinic receptors with subsequent anticholinergic effects. Has been used to reverse vagally induced symptomatic bradycardias, which may be associated with scorpion envenomation. Its use for dry secretions is debated. Will not reverse the somatic or other cranial nerve symptoms.

Vasopressors/inotropics

Used to combat hypotension refractory to IV fluid therapy.

Norepinephrine (Levophed)

Indicated for persistent hypotension not responsive to judicious fluid loading and sodium bicarbonate.

Dobutamine (Dobutrex)

Sympathomimetic amine with stronger beta than alpha effects. Increases inotropic state with afterload reduction.

Milrinone (Primacor)

Positive inotropic agent and vasodilator with little chronotropic activity.

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