We’re something of experts in spider bites in the Emergency Department. Black widow-type spider bites, however, are a little more exceptionally interesting than the average patient encounter. Latrodectism is usually nonfatal and easily managed with conservative treatment in the ED, although an immunoglobulin-based antivenom exists. Adverse effects from this antivenom are likely high-risk than any symptomatic benefit.
Now, a new antibody-fragment antivenom is vying for space on your formulary. In this study, 64 patients with clinical lactrodecism and significant baseline pain were randomized to either up to two doses of antivenin thirty minutes apart, or matching saline placebo. The primary outcome was “treatment failure”, a composite endpoint of failure to sufficiently decrease pain on the VAS scale, provision of a prescription analgesic, or a dose of the currently available antivenin.
Overall, the intervention met their predefined primary outcome – although, interestingly, half the antivenin cohort still had “treatment failure”. Then, almost a quarter of patients in the placebo cohort achieved full recovery. This remaining sliver of patients represents the measured effect size of the intervention – but the question remains the value and clinical relevance of their composite outcome. Mortality from lactrodectism is vanishingly low, and this intervention is not touted as being protective. Then, if the concern voiced by the authors is of short-term morbidity and ED recidivism in those whose pain is not adequately controlled without antivenom, then their primary, or at least a secondary outcome, ought to address this. Finally, the sample size is too small to draw any conclusion regarding safety.
This will undoubtedly be expensive and may likely expire in your hospital pharmacy prior to use. This trial gives us a small amount of information regarding its utility, but there’s little clear value demonstrated here.
“The Efficacy of Antivenin Latrodectus (Black Widow) Equine Immune F(abʹ)2 Versus Placebo in the Treatment of Latrodectism: A Randomized, Double-Blind, Placebo-Controlled, Clinical Trial”
https://www.sciencedirect.com/science/article/pii/S019606441930109X