Widow Spider Envenomation Medication

Most widow spider envenomations may be managed with opioid analgesics and sedative-hypnotics. 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 one-half hour after administration, and it has been shown to decrease the need for hospitalization.

A new antivenom (Aracmyn, manufactured by Instituto Bioclon) is about to undergo phase 3 clinical trials in the United States, but it has not yet been approved for general use. 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. Calcium gluconate is no longer recommended for widow spider envenomation. Studies suggest benzodiazepines are more efficacious than muscle relaxants for treatment of muscle pain related to widow spider envenomation. 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)

DOC 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)

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)

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

Midazolam (Versed)

Used as alternative in termination of refractory status epilepticus. Because water soluble, takes approximately 3 times longer than diazepam to peak EEG effects. Thus, clinician must wait 2-3 min to fully evaluate sedative effects before initiating procedure or repeating dose. Has twice the affinity for benzodiazepine receptors than diazepam. May be administered IM if unable to obtain vascular access.

Class Summary

Used to neutralize the toxin of a widow spider bite.

Antivenin, black widow spider

Derived from horse serum and produced by Merck & Co., Inc. Consider 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. 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 at least 20-50 mL NS. The package insert recommends intravenous injection over 15 min. However, adverse reactions may be averted by further diluting the antivenom (eg, to a total volume of 200 mL) and administering the infusion slowly (eg, over 1 h). Symptoms have been shown to improve within 1 h of antivenom administration and for as long as 48 h 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)

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

Class Summary

Prevent the histamine response in sensory nerve endings and blood vessels. More effective in preventing 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)

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