Antiviral Flu Drug Baloxavir Marboxil Succeeds in Phase 3 Study

The antiviral treatment for patients at high risk of complications from influenza met the primary objective of efficacy measured by time to improvement of symptoms compared to placebo.

The phase 3 CAPSTONE-2 study of the safety and efficacy of baloxavir marboxil in patients at high risk of complications due to influenza (flu) has met the primary objective of efficacy of a single dose of baloxavir marboxil compared to placebo as measured by time to improvement of flu symptoms. The Centers for Disease Control and Prevention defines patients at high risk of complications from influenza as adults age 65 and older or those with conditions including asthma, chronic lung disease, diabetes, or heart disease.

Baloxavir marboxil additionally performed better compared to placebo and oseltamivir for secondary endpoints including reducing the time that the virus continued to be released (viral shedding) and reducing viral levels in the body. The drug also significantly reduced the incidence of flu-related complications compared to placebo.

"Baloxavir marboxil is the first antiviral to show a clinically meaningful benefit in people who are most susceptible to complications from the flu, including older people and those living with certain medical conditions," said Sandra Horning, MD, Roche's Chief Medical Officer and Head of Global Product Development.

Roche has not yet released data from CAPSTONE-2, but results from a previous phase 3 study of baloxavir marboxil, CAPSTONE-1, are available. In CAPSTONE-1 the time to return of pre-influenza health status was just 129.2 hours for patients receiving baloxavir marboxil and 168.8 hours for patients in the placebo group.

Additionally, the percentage of patients determined positive for influenza was significantly lower in the baloxavir marboxil group compared to the oseltamivir group at 1, 2 and 4 days from baseline in virus titer.

Baloxavir marboxil is able to target A and B influenza viruses, including avian strains (e.g. H7N9, H5N1) and oseltamivir-resistant strains. The antiviral is designed to inhibit the cap-dependent endonuclease protein, an essential part of viral replication in the flu virus.

The US Food and Drug Administration (FDA) has recently accepted a New Drug Application as well as granted Priority Review to baloxavir marboxil based on the CAPSTONE-1 study and a phase 2 study. Roche expects a decision on approval by December 24, 2018.

If approved by the FDA, baloxavir marboxil would be the first single-dose oral antiviral as well as the first drug with a novel proposed mechanism of action to treat the flu in over a decade.

"We plan to submit the results of this second positive phase 3 study for baloxavir marboxil to healthcare authorities, and look forward to discussing next steps since there are no current antiviral medicines approved to specifically treat this high-risk population," added Horning.

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