The US Food and Drug Administration will undertake a priority review of Genentech’s experimental flu drug baloxavir marboxil in people aged 12 years and older.

Baloxavir marboxil is a first-in-class, single-dose investigational oral medicine with a novel proposed mechanism of action designed to target the flu virus, including oseltamivir-resistant strains and avian strains (H7N9, H5N1).

The drug is designed to inhibit the cap-dependent endonuclease protein within the flu virus, which is essential for viral replication, setting it aside from other currently available antiviral therapies.

The application contains data from the Phase III CAPSTONE-1 study, which evaluated the efficacy and safety of baloxavir marboxil in 1,436 people in the US and Japan.

This showed that the drug significantly reduced: the duration of flu symptoms by more than one day (53.7 hours versus 80.2 hours); the duration of fever by nearly a day (24.5 hours versus 42.0 hours); viral shedding (24.0 hours versus 96.0 hours); and levels of virus in the nose and throat from 24 hours through 120 hours.

The FDA is expected to make its decision by December 24, 2018.

If approved, the drug would be the first oral, single-dose antiviral and the first medicine with a novel proposed mechanism of action to treat the flu in nearly 20 years.

Baloxavir marboxil was discovered by Shionogi and is being co-developed globally by the Roche Group.