On Jan. 2, 2025, SIGA Technologies announced that its antiviral treatment TEPOXX (tecovirimat 200 mg capsules), marketed as TPOXX in the United States, had received regulatory approval in Japan for the treatment of smallpox, mpox, cowpox, as well as complications following smallpox vaccination in adults and pediatric patients weighing at least 13 kg.

TEPOXX is the first antiviral therapy approved by the Pharmaceuticals and Medical Devices Agency (PMDA), in collaboration with the Japan Ministry of Health, Labour and Welfare, for the treatment of orthopoxviruses.

The Japanese approval is based on data from 15 clinical trials of oral TEPOXX in over 800 healthy volunteers, including a pivotal repeat-dose phase 1 pharmacokinetics (PK) trial involving 20 healthy volunteers conducted in Japan. These studies showed no drug-related serious adverse events and quantifiable PK within efficacious dose ranges. Four pivotal studies in non-human primates (NHPs) and two pivotal studies in rabbits demonstrated that TEPOXX significantly reduced both mortality and viral load. The results of the animal efficacy studies were published in the July 5, 2018 issue of the New England Journal of Medicine. TEPOXX has also been studied in NHPs infected with variola virus, the virus which causes smallpox, where TEPOXX demonstrated improved survival and reduction in lesions.

TEPOXX is a highly targeted small-molecule antiviral that inhibits the VP37 protein found on the surface of all orthopoxviruses. By preventing the virus from exiting infected cells, TEPOXX slows the spread of the infection, enabling the immune system to clear the virus.

TPOXX is approved in the U.S. and Canada for the treatment of smallpox. In the European Union and United Kingdom, marketed as Tecovirimat-SIGA, it is approved for the treatment of smallpox, mpox, cowpox, and to treat complications following smallpox vaccination.