FDA approves Siga Technologies' TPOXX treatment for smallpox
SIGA Technologies announced that the U.S. Food and Drug Administration has approved oral TPOXX for the treatment of smallpox to mitigate the impact of a potential outbreak. TPOXX, a small-molecule antiviral treatment for smallpox, is the first therapy specifically approved for this indication. On May 1, 2018, the FDA's Antimicrobial Drugs Advisory Committee voted unanimously, 17 to 0, that the benefits of TPOXX outweigh its risks. Concurrent with the approval, FDA granted SIGA's request for a Priority Review Voucher. A PRV is a voucher that may be used to obtain an accelerated FDA review of a future SIGA product, or sold to a third party, and this is the first PRV awarded under the Material Threat Countermeasure PRV program enacted by the 2016 21st Century Cures Act. In addition, FDA approved a seven-year expiry for TPOXX. Under SIGA's existing contract with the Biomedical Advanced Research and Development Authority (BARDA), the company will ask BARDA to exercise an option for a $50 million payment to the company based on this extended shelf-life determination. The exercise of this option is at the sole discretion of BARDA. With the approval, SIGA is entitled to a $41 million hold back 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. FDA approval is based on data from 12 clinical trials of oral TPOXX in over 700 healthy human volunteers, which showed no drug-related serious adverse events. Four pivotal trials in non-human primates (NHPs) and two pivotal trials in rabbits demonstrated that TPOXX significantly reduced both mortality and viral load in NHP infected with monkeypox virus (MPXV) and in rabbits infected with rabbitpox virus. The results of these studies were published in the July 5, 2018 issue of the New England Journal of Medicine.