Tecovirimat (Tpoxx) is an antiviral agent that is already indicated for another orthopoxvirus, smallpox. And studies are ongoing to see if it has potential efficacy in treating monkeypox.
As of Thursday, the Centers for Disease Control and Prevention (CDC) reported there was a total of 45 confirmed monkeypox/orthopoxvirus cases in the United States.
And although there are no specific FDA approved treatments available for monkeypox infection, monkeypox outbreaks can be controlled with vaccines. On Friday, Bavarian Nordic announced the US Biomedical Advanced Research and Development Authority (BARDA) ordered an additional 500,000 doses of liquid-frozen JYNNEOS, a non-replicating smallpox vaccine and the only FDA-approved vaccine against monkeypox, for delivery in 2022. As monkeypox and smallpox stem from the same orthopoxvirus family, it's believed that some smallpox vaccines and therapies have efficacy in preventing and treating monkeypox.
The antiviral therapy, tecovirimat (Tpoxx), manufactured by SIGA Technologies, is approved for smallpox and is being studied for monkeypox treatment. The agent can be administered orally or through IV formulation for smallpox treatment. Back in May, the Food and Drug Administration (FDA) approved the intravenous (IV) formulation for smallpox and is another option for those who are unable to swallow the tecovirimat oral capsules.
“We are grateful to the FDA for their work leading to approval of IV TPOXX, which will provide access to a broader patient population,” Dennis Hruby, PhD, CSO of SIGA said at the time.
Studies using a variety of animal species have shown that tecovirimat is effective in treating disease caused by orthopoxviruses. Clinical trials in people showed the therapy was safe and had only minor side effects. In addition, tecovirimat was given to 1 patient who had monkeypox in a study that was reported in The Lancet Infectious Diseases. The patient received 600 mg of the therapy twice a day for 2 weeks and experienced a shorter duration of illness and viral shedding.
Although more studies need to be done to confirm the result, the lead investigator in the study believes the agent has potential treatment benefits.
"The single biggest takeaway is the excellent clinical and virological response to the oral antiviral tecovirimat in one patient with monkeypox who received this agent,” lead author Hugh Adler, PhD, of Liverpool University Hospitals NHS Foundation Trust told Contagion in an interview. “We definitely need well-powered, prospective studies to validate this finding, but it is a strong signal, and may be of use to clinicians managing patients with monkeypox in the current outbreak in the Western Hemisphere.”
Hruby says the therapy is being utilized for compassionate use indications at the moment.
Tecovirimat is also maintained in the US Strategic National Stockpile for smallpox. And the use of tecovirimat for monkeypox and other non-variola orthopoxvirus infections is under an expanded access IND protocol, according to the CDC.
SIGA is a commercial-stage pharmaceutical company focused on the health security market. Health security comprises countermeasures for biological, chemical, radiological and nuclear attacks (biodefense market), vaccines and therapies for emerging infectious diseases, and health preparedness.
Contagion spoke to Hruby who provided an overview about the therapy including its safety and efficacy profile, dosing regimen, its contract with BARDA, and information on some of its ongoing studies.