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Black Widow Antivenin – Does It Work?

May 6, 2019

Written by Clay Smith

Spoon Feed
Purified black widow spider antivenin was more effective for pain control than placebo and not associated with any adverse drug effects.

Why does this matter?
Black widow spider envenomation can cause severe pain and muscle spasms via latrotoxin.  Current antivenin consists of horse serum-derived antibody, which has been associated with anaphylaxis, even death.  Some have said it’s like getting an injection of “ground-up spider.”  Would a purified F(ab’)2 fragment be better and safer?

“I shall reward you with a spider goulash…”
This was a multicenter RCT that enrolled 60 patients with presumed black widow spider envenomation and moderate to severe pain to receive placebo or purified antivenin F(ab’)2 fragments.  Treatment failure (<13mm drop on visual analog scale at 60-150 minutes, receipt of commercially available antivenin, or any prescription analgesic within 48 hours post-treatment) was significantly lower in the treatment group 51.7% antivenin (15/29) vs 77.4% placebo (24/31), [-25.7, 95%CI -49.1 to -2.3, p=0.019].  Pain intensity was lower at every point in time in the antivenin group vs placebo.  There were no adverse drug effects in this small study.  This is good news for treating black widow bites, but I’ll bet this treatment won’t come cheap.  It still has >50% failure rate, which isn’t great.  On the other hand, the NNT was only 4 for complete pain relief – needing zero pain medicine out to 48h after one dose. When this comes to market, have a chat with your friendly local toxicologist before you give purified ground-up spider.

The Efficacy of Antivenin Latrodectus (Black Widow) Equine Immune F(ab’)2 Versus Placebo in the Treatment of Latrodectism: A Randomized, Double-Blind, Placebo-Controlled, Clinical Trial.  Ann Emerg Med. 2019 Mar 26. pii: S0196-0644(19)30109-X. doi: 10.1016/j.annemergmed.2019.02.007. [Epub ahead of print]

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Reviewed by Thomas Davis

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