One of the most dreaded effects of the bite of the brown recluse spider (Loxosceles spp) is the appearance of a necrotic skin lesion, but a clinical study by Brazilian researchers recently reported in PLOS Neglected Tropical Diseases shows that the problem can be solved by administering antivenom, especially if this is done within 48 hours of the incident.

An antivenom produced by Butantan Institute, an arm of the São Paulo State Department of Health, was used in the study. As the authors of the paper explain, there is no consensus regarding the best treatment to avoid necrosis and ulceration in cases of brown recluse spider bites.

A 2009 study involving rabbits showed that necrotic lesions were approximately 30% smaller even when the antivenom was administered 48 hours after the animals were bitten.

“However, until now there haven’t been any clinical studies showing whether this antivenom could prevent cutaneous necrosis, or even how long after the incident it should be administered,” said Ceila Maria Sant’Ana Málaque, first author of the paper. Málaque is a physician who specializes in treating patients bitten by venomous animals and with infectious and parasite-borne diseases at Butantan Institute’s Vital Brazil Hospital and the intensive care unit (ICU) of Emílio Ribas Institute of Infectious Disease.

To answer these questions, researchers at Vital Brazil Hospital conducted a six-year prospective observational study (November 2014-November 2020) involving 146 patients, 74 of whom received the antivenom.

“Because use of antivenom is recommended by the Handbook on Diagnosis and Treatment of Envenomation [published by FUNASA, Brazil’s National Health Foundation], we were unable to conduct a double-blind randomized study and therefore analyzed the patients who received the antivenom on admission to the hospital and before the appearance of skin necrosis,” Málaque said. 

The control group comprised patients who were admitted more than 48 hours after they were bitten and did not receive the antivenom.