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Our lead product, TPOXX (tecovirimat), is a highly targeted antiviral treatment against orthopoxviruses, including smallpox.  


Our Path to Approval and Use

Mpox is a serious disease caused by the monkeypox virus that continues to spread throughout the world, presenting a threat to global health. While available vaccines can be effective at preventing mpox, protection is neither complete nor durable, leaving patients vulnerable to disease progression and transmission.


In the U.S., TPOXX is an antiviral drug not currently approved by the FDA for the treatment of mpox, but it is used to treat patients with mpox through an expanded access investigational new drug protocol held by the U.S. Centers for Disease Control and Prevention (CDC).


The CDC recommends that patients who have presumed or laboratory-confirmed mpox should speak with a healthcare provider about enrolling in the Study of Tecovirimat for Human Mpox Virus (STOMP) clinical trial. The STOMP trial is being conducted to evaluate the efficacy of TPOXX for the treatment of mpox. Patients do not need to have severe disease or be at high risk of severe illness to enroll in the study.


For patients who are not eligible to enroll in STOMP or decline enrollment, healthcare providers can contact their state or territorial health department to ask about stockpiled oral tecovirimat that is available under the CDC’s tecovirimat expanded access investigational new drug protocol.


See more information about access options

TPOXX donations are also used to support emergency use in low-and-middle-income countries, including DRC and other countries on the African continent with mpox cases.

Regulators in African countries require randomized clinical trials demonstrating efficacy and drug approval before TPOXX (tecovirimat) can be used routinely in clinical and public health practice. Should mpox studies deliver results that contribute to TPOXX (tecovirimat) approval as treatment for mpox in these countries, SIGA is committed to making TPOXX (tecovirimat) available on an affordable basis for mpox-related indications in low-income countries.

Access to TPOXX for mpox

How TPOXX Works

Mpox is a serious disease caused by the monkeypox virus that continues to spread throughout the world

Developing a drug for which there are no human cases requires innovative clinical and regulatory strategies. With smallpox eradicated in 1980, it is unethical to conduct efficacy testing in human trials. Consequently, TPOXX was evaluated using a novel development path based on the FDA’s “Animal Rule,” in which safety studies were conducted in healthy human volunteers and efficacy and toxicology studies were conducted in animal models. The FDA also granted TPOXX Fast Track and Orphan Drug Designation.

TPOXX was among the first novel small molecule therapies delivered to the Strategic National Stockpile (SNS) under Project BioShield, a U.S. government program designed to accelerate the research, development, purchase, and availability of effective medical countermeasures against biological, chemical, radiological, and nuclear (CBRN) agents. TPOXX’s advanced development has been funded in partnership with the Biomedical Advanced Research and Development Authority (BARDA) of the U.S. Department of Health and Human Services.

Naturally-occurring smallpox has been successfully eradicated through global vaccine campaigns. Despite this important public health achievement, there is an enduring concern that smallpox could be used as a bioweapon. DNA synthesis technology and the possibility of unaccounted for smallpox stocks pose significant risks. While there are two acknowledged stocks of smallpox virus held by the U.S. and Russia, some believe that additional stores of the virus could be in the hands of governments or organizations that might use them to cause harm. The DNA sequence of the smallpox genome is in the public domain and could be synthesized in a laboratory from scratch or created by genetically modifying a similar virus (e.g., camelpox).​

A smallpox bioterror attack could be especially damaging because the majority of today’s population is not immune to the virus, as routine vaccination ended in the 1970s. Vaccination alone would likely not be effective in the event of a smallpox bioterror attack. The vaccine must be administered within 5 days following infection to be therapeutically effective, but symptoms do not appear until 14 days post infection. When combined with social media-escalated disinformation and vaccine hesitancy, these limitations underscore the need for an effective smallpox antiviral therapy. As the first antiviral agent specifically indicated for the treatment of smallpox, TPOXX would play a critical role in responding to a smallpox bioterror attack.

Oral TPOXX® (tecovirimat) is the first drug approved by the U.S. Food and Drug Administration (FDA)

Smallpox is one of the world’s deadliest threats and cannot be addressed with vaccines alone.  Both medicines and vaccines are essential to combat orthopoxviruses.


Oral TPOXX (tecovirimat) is the first drug approved by the U.S. Food and Drug Administration (FDA) specifically indicated for treating smallpox disease in adults and pediatric patients weighing at least 13 kg. Following U.S. approval, Health Canada also authorized the use of oral TPOXX to treat smallpox disease in adults and pediatric patients weighing at least 13 kg. Oral TPOXX, under the brand name Tecovirimat-SIGA, was later approved by the European Medicines Agency (EMA), the Norwegian Medicines Agency, and the Medicines and Healthcare products Regulatory Agency (MHRA-UK) for the treatment of smallpox, mpox, cowpox, and vaccinia complications following vaccination against smallpox in adults and children weighing at least 13kg.

U.S. - See FDA Prescribing Information

Canada - See Health Canada Prescribing Information
Europe - See EMA Prescribing Information
U.K. - See MHRA Prescribing Information

TPOXX Injection, the intravenous (IV) formulation of TPOXX, has been approved by the FDA for the treatment of smallpox in patients weighing at least 3 kg. This important option will allow patients who are too sick to swallow oral capsules to receive treatment. Healthcare providers can click here for important prescribing information on proper preparation and administration of TPOXX Injection.

TPOXX® specifically inhibits the activity of a protein called VP37, found on the surface of all orthopoxviruses.

TPOXX specifically inhibits the activity of a protein called VP37, found on the surface of all orthopoxviruses. This prevents the virus from leaving infected cells, slowing the spread of the infection and limiting it to a point where the immune system can clear the virus. 


Oral TPOXX is considered safe and well-tolerated in patients. The safety profile can be attributed to the targeted nature of the drug, which limits adverse reactions. Despite the lack of controlled clinical trial data that demonstrate efficacy in humans, TPOXX was proven to be effective in animal models of smallpox, mpox, and other orthopoxviruses.

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