FDA approves first drug to treat smallpox in efforts to thwart bioterrorism

The US Food and Drug Administration (FDA) has approved the first drug indicated to treat smallpox — TPOXX (tecovirimat) — to SIGA Technologies.

Although smallpox was eradicated in 1980 it is classed by the World Health Organisation (WHO) as a contagious and sometimes fatal infectious disease and there are concerns that it could be employed as a bioweapon.

“To address the risk of bioterrorism, congress has taken steps to enable the development and approval of countermeasures to thwart pathogens that could be employed as weapons. Today’s approval provides an important milestone in these efforts. This new treatment affords us an additional option should smallpox ever be used as a bioweapon,” said FDA commissioner Dr Scott Gottlieb. “This is the first product to be awarded a Material Threat Medical Countermeasure priority review voucher. Today’s action reflects the FDA’s commitment to ensuring that the US is prepared for any public health emergency with timely, safe and effective medical products.”

Smallpox (caused by the variola virus) was spread mainly through direct contact between people with symptoms occurring about 10–14 days after infection and included fever, exhaustion, headache and backache. A rash of small, pink bumps would be the initial stage, which progressed to pus-filled sores before crusting over and scarring. Complications of the disease could include encephalitis (inflammation of the brain), corneal ulcerations and blindness.

The newly approved treatment, TPOXX, has been evaluated for effectiveness in animal studies, where animals were infected with viruses that are closely related to the virus that causes smallpox. The main outcome measured was survival rate, which was higher in the animals treated than those that had been given a placebo.

This approval has been made under the FDA’s Animal Rule, which allows efficacy findings from adequate and well-controlled animal studies to support an FDA approval when it is not feasible or ethical to conduct efficacy trials in humans.

Additionally, the drug has been evaluated in 359 healthy human volunteers, without smallpox infection. Side effects that were most frequently reported included headache, nausea and abdominal pain.