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Tackling Monkeypox With Tecovirimat
Volume 18, Issue 2
Over 2 years into the COVID-19 pandemic, and the United States is now facing a new public health crisis. Monkeypox—an orthopoxvirus that is endemic to parts of Western Africa—has been spreading in various hotspots in the United States, mostly among men who have sex with men.
Monkeypox does have an effective vaccine; however, efforts to distribute the vaccine to outbreak areas in the United States have been slow. There are no FDA-approved treatments for monkeypox, but tecovirimat is available under compassionate use.
In this week’s issue of Talking Therapeutics, we cover some of the background basics of this investigational agent:
Tecovirimat was FDA approved for smallpox in 2018 under the animal efficacy rule, or the “Animal Rule.” This rule is used when drug efficacy cannot be reasonably established in humans, which is the case with smallpox as the disease has been eradicated.
Efficacy data was hence derived from animal studies of infections from related viruses, like monkeypox in nonhuman primates. The safety data for tecovirimat was derived from testing in healthy human volunteers.
The American College of Clinical Pharmacology states, “Tecovirimat targets and inhibits the activity of the orthopoxvirus VP37 protein (encoded by and highly conserved in all members of the orthopoxvirus genus) and blocks its interaction with cellular Rab9 GTPase and TIP47, which prevents the formation of egress-competent enveloped virions necessary for cell-to-cell and long-range dissemination of virus.”
For treating smallpox in humans, the recommended dose is 600 mg orally, twice daily, and the recommended duration of therapy is 14 days. Investigators determined these by studying plasma concentrations of tecovirimat in healthy volunteers vs animal models “at doses that had been shown to have full effectiveness against monkeypox and rabbitpox,” said researchers in The New England Journal of Medicine.
Although there are case reports of using tecovirimat to treat patients with monkeypox and other orthopoxvirus infections, these data are insufficient to demonstrate efficacy.
In response to the current outbreak, the NIH is now also developing a US-based randomized controlled trial to assess the safety and efficacy of tecovirimat for the treatment of monkeypox disease. Until this study is completed, the use of tecovirimat will be restricted to compassionate use, and patients need to understand that the range of outcomes from using this drug to treat monkeypox infections includes benefit, no effect, and harm.
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