The U.S. Food and Drug Administration (FDA) has granted priority review to a new antiviral drug that has been shown to notably reduce the duration of influenza symptoms. This single-dose drug is fast-acting and will potentially be approved for use in the United States by the end of 2018.

In development for several years, baloxavir marboxil has an entirely novel mechanism of action, unlike any other previously produced anti-influenza medication. Inside the human body the drug metabolizes into baloxavir acid, a compound that inhibits a key enzyme called influenza polymerase. Without this enzyme the influenza virus struggles to replicate.

A comprehensive Phase 3 study on the drug's efficacy was recently completed and the successful results spurned the FDA to grant it Priority Review status, meaning the application will be resolved within six months.

The results from the human trial into the drug's efficacy suggest it could be an incredibly useful new tool in a doctor's arsenal. Compared to a placebo, the drug reduced the duration of flu symptoms by over a day (median time 53.7 hours versus 80.2 hours), and reduced the duration of fever to just 24 hours (median time 24.5 hours versus 42.0 hours).

As well as shortening the overall duration of the infection, an even more impressive effect of the drug was its ability to reduce the time a person is infectious to others. The trial indicated the drug lowers the duration of what is referred to as "viral shedding" from an average of 96 hours to just 24 hours. This remarkable effect could significantly reduce the ability of the virus to travel from person to person and be important in the case of localized influenza outbreaks.

It has been almost 20 years since a new antiviral drug targeting influenza hit the market. In 1999 oseltamivir (better known as Tamiflu) was approved for clinical use, but due to its cost and adverse side effects it was never deployed broadly for average healthy people.

Baloxavir marboxil was compared to oseltamivir in its Phase 3 trials and, while it displayed similar efficacy in reducing overall duration of flu symptoms, its viral shedding effect dramatically outperformed oseltamivir. Another major benefit over oseltamivir is that baloxavir marboxil is a single-dose medicine, unlike oseltamivir, which is administered twice a day for five days. The big caveat is that this new drug still needs to be administered within the first 48-hours of symptoms appearing.

The drug has already been approved for use in Japan and is being marketed in that country under the brand name Xofluza. It is unclear how much the drug will cost when approved in the United States but in Japan a dose costs about US$43.50, a reasonable price for a one-and-done medication. At this stage the drug is only approved for use in persons over the age of 12, but further pediatric trials are currently underway to establish safety and efficacy in younger patients.

Source: Roche