With Looming Bioterrorism Threats, FDA Approves First Smallpox Therapeutic

Small Pox

Shares of SIGA Technologies soared more than 11 percent late Friday after the company announced that its smallpox treatment Tpoxx was approved by the U.S. Food and Drug Administration (FDA). This is the first approved treatment for the disease that at one time was believed to have been eradicated, but due to the threat of bioterrorism has become an increased concern for the world.

Because of the bioterrorism threats, the government pushed for the development of medical countermeasures to the dreaded disease. While vaccines are important, the government believed there should be a therapeutic available to reduce the chance of mass deaths should a bioweapon be used. After the prevalence of the smallpox vaccine, the last outbreak of the deadly disease that occurred in the United States was in 1949. The disease had been declared eradicated by the World Health Organization in 1980

The FDA greenlit Tpoxx based on data from six different trials involving animals. Four trials involved primates and two involved rabbits. The primates were infected with monkeypox virus and the rabbits were infected with rabbitpox. The trials demonstrated that Tpoxx “significantly reduced both mortality and viral load” in the animals. The results of these studies were published in the July 5, 2018 issue of the New England Journal of Medicine.

Siga said that the FDA’s approval came two months after the agency’s Antimicrobial Drugs Advisory Committee voted unanimously, 17 to 0, in support of the medication. Siga used a Priority Review Voucher in order to gain an accelerated review of its medicine. The accelerated review marked the first time that was used under the Material Threat Countermeasure PRV program enacted by the 2016 21st Century Cures Act, Siga said in its announcement. Tpoxx (tecovirimat) was approved in order to mitigate the impact of a potential outbreak, the company said.

“The FDA approval of TPOXX achieves an important objective for both SIGA and our lead partner in the U.S. Government, the Biomedical Advanced Research and Development Authority (BARDA).  The approval validates this novel smallpox therapy as an important medical countermeasure in response to a potential smallpox outbreak,” Siga Chief Executive Officer Phil Gomez said in a statement.

Siga’s Tpoxx was developed with support from the Biomedical Advanced Research and Development Authority (BARDA). With the FDA approval, Siga said it will ask BARDA to exercise an option for a $50 million payment to the company based on this extended shelf-life determination. With the approval, SIGA is entitled to a $41 million holdback payment under the existing contract with BARDA, provided that BARDA confirms that there is no difference between the approved product and the courses of TPOXX that have already been delivered to the Strategic National Stockpile (SNS), the company said in its announcement.

Tpoxx will be available for use through the U.S. government’s Strategic National Stockpile. There have been about two million doses of the treatment delivered to the stockpile, the company said.  

Siga said some members of the Antimicrobial Drugs Advisory Committee suggested that there could be additional uses for Tpoxx, including prophylactic use in individuals exposed to smallpox and other orthopoxviruses, such as monkeypox, which can jump that species barrier. Siga said it will examine these potential markets and the feasibility of expanding the TPOXX label to include these indications.

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