Tecovirimat, known by its brand name TPOXX, is an antiviral medication developed as a measure against specific viral threats. It was created to address concerns about the potential use of certain viruses as bioweapons and is a component of public health preparedness strategies, held for use during public health emergencies. Its development and approval process were unique, relying on specific regulatory pathways designed for situations where human efficacy trials are not ethical or feasible.
Approved and Investigational Uses
Tecovirimat is officially approved by the U.S. Food and Drug Administration (FDA) for the treatment of smallpox, a highly contagious disease that was declared eradicated in 1980. This approval was granted under the FDA’s “Animal Rule,” which allows for authorization based on successful animal studies when human trials would be unethical.
Beyond its primary indication, tecovirimat is used investigationally to treat other related viruses in the orthopoxvirus family. It has been most notably deployed under an Expanded Access Investigational New Drug (EA-IND) protocol for mpox (formerly monkeypox) infections. This allows access for patients with severe disease or those at high risk for severe outcomes, such as individuals who are severely immunocompromised, pregnant, or children.
The drug is also indicated in Europe and considered for use in the United States for treating cowpox and complications that can arise from the vaccinia virus, which is used in the smallpox vaccine. While clinical trials have been conducted to evaluate its effectiveness for mpox, initial findings suggest that while safe, it may not significantly speed up the healing of lesions in most patients. Treatment is therefore often prioritized for those with the most serious or life-threatening manifestations of the disease.
Mechanism of Action
Tecovirimat functions by preventing a virus from spreading from an infected cell to healthy ones. It is classified as a viral egress inhibitor, meaning it stops the virus from exiting the cell it has hijacked. The drug specifically targets a protein known as p37, which is found on the surface of orthopoxviruses. This protein is responsible for creating the mature, enveloped form of the virus that is capable of transmission.
By binding to and inhibiting the p37 protein, tecovirimat effectively traps the newly formed virus particles inside the infected cell. This action prevents the virus from completing its lifecycle and spreading throughout the body to infect more cells.
This mechanism halts the progression of the infection, giving the body’s immune system a better chance to control and clear the virus. This targeted approach is effective against all orthopoxviruses because they share the p37 protein, including the viruses that cause smallpox, mpox, and cowpox.
Administration and Dosing
Tecovirimat is available in two forms: oral capsules for most patients and an intravenous (IV) formulation for individuals who are unable to swallow pills. The standard course of treatment for either form is 14 days. The oral capsules, which each contain 200 mg of the drug, must be taken within 30 minutes of eating a full meal that is moderate to high in fat, as this helps the body absorb the medication properly.
The specific dosage is based on the patient’s weight. For adults and children weighing between 40 kg and 120 kg, the oral dose is 600 mg taken twice daily. For patients who require the IV version, the infusion is administered over six hours. If a patient starts on IV tecovirimat, they are switched to the oral capsules as soon as they can tolerate them to complete the 14-day treatment course.
Side Effects and Safety Profile
Tecovirimat is considered to be a well-tolerated medication. The most common side effects reported during clinical studies with healthy volunteers were headache, nausea, and abdominal pain. In studies involving human subjects, there were no serious adverse events determined to be related to the drug itself.
The safety profile was established through trials in healthy human participants, as it was not ethical to conduct efficacy studies for smallpox in people. For its investigational use in mpox, data from clinical trials also showed the drug to be safe.
Access and Availability
Tecovirimat is not a medication that can be picked up at a local retail pharmacy. The vast majority of the supply is held in the U.S. Strategic National Stockpile (SNS) to be deployed in the event of a large-scale public health emergency, such as a smallpox outbreak.
For individual cases of mpox or other non-variola orthopoxvirus infections, access is tightly controlled. A healthcare provider must request the drug for an eligible patient through their state or local public health department. This process operates under a CDC-held protocol known as an Expanded Access Investigational New Drug (EA-IND), sometimes referred to as “compassionate use.”
This pathway is specifically for patients who meet certain criteria, such as having severe disease or being at high risk for it. The CDC reviews these requests to authorize the release of the drug from the SNS. This centralized system ensures the medication is used appropriately for its investigational purposes while being reserved for its primary role in biodefense.