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Anti-venom drug gains FDA approval despite clinical trial tribulations

Despite significant difficulties, a new anti-venom product that treats the pain (and the neurological side effects) of a bark-scorpion sting was approved by the Food & Drug Administration after testing in a tiny clinical trial.

Bark-scorpion stings, which are potentially lethal, can lead to severe pain, extreme nausea, blurred vision and breathing problems in children, according to a Nature Spoonful of Medicine blog post. The only anti-venom product that existed before its invention did not have FDA approval, and, because it was not highly purified, often caused anaphylactic reactions. What's more, its production ended in 2000, and supplies in hospitals were dwindling.

When VIPER Institute researchers developed Anascorp, they already had an idea of how effective it was. Still, designing a normal-sized clinical trial for an anti-venom is particularly challenging for ethical reasons. Since scorpion stings can't be predicted (and no clinical trial would voluntarily expose children to venomous scorpions), there was no way to enroll participants ahead of time. VIPER director Leslie Boyer, MD, searched for hospitals willing to participate, with ultimately positive results:

In the end, Boyer found just two hospitals in Tucson prepared to participate. Between May 2004 and October 2005, she and her colleagues treated 15 children as part of the trial, mostly under the age of six. Even with the small sample size, the results were striking: symptoms of the scorpion's neurotoxin resolved within four hours for all eight children receiving Anascorp, whereas only one of seven subjects receiving placebo recovered so quickly. The rest received heavy doses of sedatives and had to stay for longer in intensive care units before it was deemed safe enough to discharge them from the hospitals.

Considering it unethical to continue giving children placebo treatments, researchers, who still wanted to prove Anascorp's safety and effectiveness, launched an open-label trial. They treated over 200 children by 2010 in what had become the world's largest anti-venom study. The FDA's recent approval may be a milestone in a delicate process: ethically deriving a statistically significant result from a minuscule population.

Photo by Charles & Clint

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