Smallpox antiviral approved under FDA’s Animal Rule

Regulatory NewsRegulatory News
| 07 June 2021 | By Kari Oakes 

Though the World Health Organization declared smallpox eradicated in 1980, FDA has approved Tembexa (Chimerix,brincidofovir) as a treatment for the contagious, deadly disease caused by the variola virus.
The 4 June announcement of Tembexa’s approval noted that smallpox drug development is “an important component of the US medical countermeasures response,” since the federal government has significant concerns about the virus’ potential use as a bioweapon. Tembexa was developed as part of the smallpox antivirals program at the Department of Health and Human Service’s Biomedical Advanced Research and Development Authority (BARDA).
The approval was based on studies that involved neither humans nor the variola virus. Given the ethical unacceptability that a human trial would entail, and the risks inherent in any studies that induce variola infection, such a trial would have been infeasible.
Instead, the drug was approved under FDA’s Animal Rule. This provision addresses situations where medical countermeasures are necessary, but human challenge studies are not possible. A provision of the Food, Drug & Cosmetics Act, known as section 565(d), came in 2013 as part of a suite of pandemic preparedness provisions. Under section 565(d), sponsors for drugs and devices falling under this situation may request one meeting with FDA to discuss “proposed animal model development activities” and a second meeting before they start pivotal animal studies.
FDA maintains a compliance program for inspection of nonclinical labs that conduct Animal Rule-specific studies and has developed guidance documents for product development under the Rule, as well as other resources.
Brincidofovir is also being developed to treat cytomegalovirus and adenovirus infections that are associated with bone marrow transplantation; these studies were the source of safety data for Tembexa. BARDA’s smallpox antiviral program has also moved another drug, dubbed ST-246 (SIGA), to the strategic national stockpile. That drug would be available under emergency use authorization or via contingency mechanisms authorized by the Centers for Disease Control or the Department of Defense.
According to BARDA, two other smallpox antivirals that attack the variola virus through different mechanisms of action are currently being developed, “to mitigate emergence of potential drug resistance.”


© 2022 Regulatory Affairs Professionals Society.

Tags: Animal, BARDA, FDA, Rule, US

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