Pharmacist Insights: Baloxavir Marboxil (Xofluza)

In 2019, the FDA approved single-dose baloxavir marboxil (Xofluza, Genentech) for use in patients who are at a high risk of developing influenza-related complications.

The FDA initially approved baloxavir marboxil in October 2018 for the treatment of acute, uncomplicated influenza in patients aged 12 years and older who have been symptomatic for no more than 48 hours. The approval marked the first new antiviral flu treatment with a novel mechanism of action backed by the agency in nearly 20 years.

Baloxavir marboxil was the first antiviral medication approved specifically for this use. Baloxavir marboxil has a novel mechanism of action that inhibits polymerase acidic endonuclease, which is an enzyme essential for viral replication.

Individuals with chronic conditions or those aged 65 years and older are typically at a higher risk of developing flu complications, which can range from sinus or ear infections to more serious events, such as pneumonia.

The supplemental New Drug Application approval was based on results from the phase 3 CAPSTONE-2 study, which included individuals aged 12 years and older who were at high risk of complications from the flu. The study compared a single dose of 40 mg or 80 mg of baloxavir marboxil with oseltamivir (75 mg twice daily for 5 days), versus placebo.

According to the data, baloxavir marboxil significantly reduced time to improvement of flu symptoms compared with placebo in those at high risk of complications (median time 73 hours versus 102 hours; p<0.001). Additionally, similar efficacy results were observed between baloxavir marboxil and oseltamivir in relation to duration of symptoms (median time 73 hours versus 81 hours).

For those with type B virus, the median time to improvement of flu symptoms was shorter in the baloxavir marboxil compared with the placebo group (75 hours versus 101 hours, respectively).

Overall, adverse events reported in the study included diarrhea, bronchitis, nausea, sinusitis, and headache. Baloxavir marboxil was generally well tolerated, with no new safety signals identified.