Widow Spider Envenomation Medication

Updated: May 28, 2020
  • Author: Sean P Bush, MD, FACEP; Chief Editor: Joe Alcock, MD, MS  more...
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Medication Summary

Most widow spider envenomations may be managed with opioid analgesics and sedative-hypnotics. Antihypertensives are recommended for refractory hypertension in pregnancy and in patients with coronary artery disease, cerebrovascular disease, or other severe vascular disease.

Antivenom may be indicated for patients who have severe envenomations with pain refractory to these measures. Antivenom should be considered when envenomation seriously threatens pregnancy or precipitates potentially limb- or life-threatening effects (eg, severe hypertension, unstable angina, priapism, compartment syndrome). [13] On average, antivenom administration results in resolution of most symptoms within 60 minutes of administration, and it has been shown to decrease the need for hospitalization.

However, the Redback Antivenom Evaluation II (RAVE-II) study from Australia in 2014 reported that adding antivenom to standard analgesia did not significantly improve systemic symptoms or pain in patients with redback spider bite and severe pain, with or without systemic symptoms. [21] After 2 hours, 38 (34%) of 112 patients from the antivenom group had clinically significant improved pain, versus 26 (23%) of 112 in the placebo group (95% confidence interval, -1.1% to 22.6%; P = .10). For systemic symptoms, they resolved after 2 hours in 9 (26%) of 35 patients in the antivenom group, versus 9 (22%) of 41 in the placebo group (95% confidence interval, -15% to 23%; P = .79). 

A new antivenom, Latrodectus immune F(ab’)2 (or Anawidow, previously known as Analatro, manufactured by Instituto Bioclon) has undergone phase 3 clinical trials in the United States but has not yet been approved for general use. [22] It may be associated with less risk of allergic reaction than the existing antivenom, so its indications for use may differ from the current indications. [22, 23]

Calcium gluconate is no longer recommended for widow spider envenomation.

Studies suggest benzodiazepines are more efficacious than other muscle relaxant agents for the treatment of muscle pain related to widow spider envenomation.

Prophylactic antibiotics are not indicated.



Class Summary

Pain control is essential to quality patient care. It ensures patient comfort and promotes pulmonary toilet. Most analgesics have sedating properties that are beneficial for patients who have sustained trauma.

Morphine sulfate (Duramorph, Infumorph, Astramorph injections)

Morphine sulfate is the drug of choice for narcotic analgesia because of its reliable and predictable effects, safety profile, and ease of reversibility with naloxone. Morphine sulfate administered IV may be dosed in a number of ways and commonly is titrated to the desired effect.



Class Summary

By binding to specific receptor sites, these agents appear to potentiate the effects of gamma-aminobutyrate (GABA) and to facilitate inhibitory GABA neurotransmission and other inhibitory transmitters.

Lorazepam (Ativan)

Lorazepam is a sedative hypnotic in the benzodiazepine class that has a short onset of effect and relatively long half-life. By increasing the action of GABA, a major inhibitory neurotransmitter in the brain, it may depress all levels of the CNS, including the limbic and reticular formation.

Diazepam (Valium)

Diazepam depresses all levels of the CNS (eg, limbic and reticular formation), possibly by increasing the activity of GABA. It is a third-line agent for agitation or seizures because of a shorter duration of anticonvulsive effects and accumulation of active metabolites that may prolong sedation.

Midazolam (Versed)

Midazolam is used as an alternative in the termination of refractory status epilepticus. Because it is water soluble, it takes approximately 3 times longer than diazepam to peak EEG effects. Thus, the clinician must wait 2-3 minutes to fully evaluate the sedative effects before initiating a procedure or repeating a dose. Midazolam has twice the affinity for benzodiazepine receptors than diazepam. It may be administered intramuscularly if vascular access cannot be obtained. Intranasal midazolam is an option for pediatric widow spider envenomation.



Class Summary

These are used to neutralize the toxin of a widow spider bite. Obtain informed consent before antivenom administration, if possible.

Antivenin, black widow spider

Black widow spider antivenin is derived from horse serum and produced by Merck & Co., Inc. Consider it for patients with grade 2 or grade 3 envenomations who are refractory to opiates and sedative-hypnotics and do not have risk factors for immediate hypersensitivity reactions. Some authorities advocate antivenom administration for certain patient groups, such as children and elderly persons. The package insert recommends skin testing for possible allergic reaction to the antivenom.

To mix the antivenom, dissolve 1 vial in 2.5 mL of sterile diluent with gentle agitation, then dilute this into a total volume of 50 mL normal saline. The package insert recommends intravenous injection over 15 minutes. Symptoms have been shown to improve within 1 hour of antivenom administration and for as long as 48 hours or more after envenomation.

In Australia, antivenom for Latrodectus envenomation is available from Commonwealth Serum Laboratories and, in South Africa, from the South African Institute of Medical Research. Indications for antivenom use and routes of administration vary around the world.



Class Summary

Tetanus immunization should be instituted following a black widow spider bite. Tetanus results from elaboration of an exotoxin from Clostridium tetani. A booster injection in previously immunized individuals is recommended to prevent this potentially lethal syndrome. Patients who may not have been immunized against C tetani products (eg, immigrants, elderly persons) should receive tetanus immune globulin (Hyper-Tet).

Diphtheria-tetanus toxoid (dT)

Diphtheria-tetanus toxoid is used for the passive immunization of any person with a wound that might be contaminated with tetanus spores.



Class Summary

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

Antihistamines act by competitive inhibition of histamine at the H1 receptor, which mediates the wheal and flare reactions, bronchial constriction, mucous secretion, smooth muscle contraction, edema, hypotension, CNS depression, and cardiac arrhythmias.

In the treatment of black widow spider envenomations, antihistamines are used before antivenom administration to reduce acute adverse reactions to the antivenom.

Diphenhydramine (Benadryl)

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