Black widow spider bites, while rare enough in the actual world, are often present at ABEM General. How many know what to do for these patients when they present to the ED?
The most common answer given is IV calcium gluconate. Well, according to Clark et al., the NNT is 25 as only 4% got relief with that treatment. Given that it can be caustic to veins, and the benefit is negligible, you probably don’t want to be giving it.
Benzos and opioids are more effective for treatment of the pain and muscle spasm. Antivenin is even more effective, as well as significantly decreasing length of stay in the hospital. However, the cost of the antivenom may be more than the cost of hospitalization, so you may want to reserve it for people with other systemic medical problems. Be wary of the allergic or atopic patient, as the only death in that series was an asthmatic who was given IV push antivenom instead of the usual drip.
Clark RF, Wethern-Kestner S, Vance MV, Gerkin R. Clinical presentation and treatment of black widow spider envenomation: a review of 163 cases. Ann Emerg Med. 1992 Jul;21(7):782-7. [PMID 1351707]
For those that didn’t know, the current equine latrodectus antivenom is so old that it predates the FDA, and thus has grandfathered approval. It does appear significantly safer than the old Wyeth equine crotalid antivenom.
A word about magnesium. You aren’t a real emergency doctor if you haven’t seen a medical condition and thought, “yeah, a little magnesium could treat that.” Well, the literature is lacking for magnesium, so don’t expect an endorsement here. The only paper I’ve found that I can read (my German and Russian is lacking) isn’t even on pubmed, so you have to look for it. And then when you read it, you don’t get that part of your life back, as it is a 4 patient case series that shouldn’t be practice changing.
Cesareo DA. “Red back” spider bite and magnesium sulphate treatment. American Journal of Tropical Medicine and Hygiene. 1934;14:33–44
EBM Gone Wild