Is there a role for antivenom in treating black widow spider bites?

April 14, 2012, 5:17 pm


Examination of adverse events following black widow antivenom use in California. Nordt SP et al. Clin Toxicol 2012 Jan;50:70-73.


Although the bite of the black widow spider (genus Latrodectus) is widely feared and can cause significant local and muscular pain, there has never been a death reported in the United States caused by this envenomation. An effective antivenom has been available since 1954, but can cause anaphylaxis. Some clinicians are reluctant to use a potentially fatal antivenom to treat a non-lethal condition, and prefer to control symptoms of pain and muscle rigidity with opiates and benzodiazepines.

This study retrospectively reviewed cases of black widow spider bite treated with black widow antivenom in the California Poison Control System electronic database, identifying 96 eligible patients. The most common signs and symptoms recorded included generalized pain (91%), local erythema (57%). muscle cramping/rigidity (43%), and abdominal pain (41%). Seventy-five patients (78%) received opioids and 69 patients (72%) received benzodiazepines.

Every patient but one received only 1 vial of antivenom. In all cases, pain relief after antivenom administration was documented. One patient developed dermal flushing and one developed urticaria during administration of antivenom. In the latter case, the infusion was stopped and  the patient treated with diphenhydramine. There were no deaths, and no patient developed dyspnea, wheezing, angioedema, or hypotension.

The authors note that black widow spider antivenom is a low-cost therapy, with the wholesale price of 1 vial being $33.25. They conclude:

The low rate of adverse effects and no severe allergic reactions suggests that Black Widow Spider Antivenin (Merck) appears to be safe when one vial was administered to both pediatric and adult patients.

The also state that there has been only a single case of death reported following administration of the antivenom since it became available in 1954. The note that in that case the antivenom was administered in a completely inappropriate manner: given by IV push (instead of slow infusion as recommended) to a patient with atopy, asthma, and multiple drug allergies. Actually, there was recently another fatality associated with this antivenom reported by the National Poison Data System in 2010. In that case, the antivenom was administered to a patient with asthma who apparently did not receive an adequate trial of symptomatic therapy.

To read my just-published Emergency Medicine News column about this case — and about a recent debate between Dr. Sean Nordt and Dr. Billy Mallon about the role of antivenom in treating black widow spider bites — click here.

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