Baloxavir Marboxil Approved for Postexposure Prophylaxis of Influenza

The approval was supported by data from the randomized, double-blind, placebo-controlled phase 3 Blockstone trial.

The Food and Drug Administration (FDA) has expanded the approval of Xofluza (baloxavir marboxil; Genentech) to include postexposure prophylaxis of influenza in persons 12 years of age and older following contact with an individual who has influenza.

The approval was supported by data from the randomized, double-blind, placebo-controlled phase 3 BLOCKSTONE trial that assessed the efficacy and safety of Xofluza in 607 participants aged 12 years and older who were exposed to an individual with influenza in their household. Participants were randomized 1:1 to receive either a single dose of Xofluza or placebo. The primary end point was clinical influenza, as confirmed by reverse-transcriptase-polymerase-chain-reaction testing, over a period of 10 days.

Results showed a statistically significant reduction in the proportion of household contacts with laboratory-confirmed clinical influenza from 13% in the placebo group to 1% in the Xofluza group. As for safety, Xofluza was found to be well tolerated with no new safety signals. The most common adverse events reported with Xofluza included diarrhea (3%), bronchitis (3%), nausea (2%), sinusitis (2%) and headache (1%).

“This expanded indication for Xofluza will provide an important option to help prevent influenza just in time for a flu season that is anticipated to be unlike any other because it will coincide with the coronavirus pandemic,” said Debra Birnkrant, MD, director of the Division of Antiviral Products in the FDA’s Center for Drug Evaluation and Research.

Xofluza is already approved for the treatment of acute uncomplicated influenza in patients aged 12 years and older who have been symptomatic for no more than 48 hours and who are otherwise healthy, or at high risk of developing influenza-related complications. The treatment is supplied as 20mg and 40mg tablets. A new granule formulation for oral suspension (2mg/mL) has also been approved for patients who are unable to or have difficulty swallowing tablets, or for those who require enteral administration.


1.    FDA expands approval of influenza treatment to post-exposure prevention. [press release]. Silver Spring, MD: US Food and Drug Administration; November 23, 2020. 

2.    Genentech announces FDA approval of Xofluza for the prevention of influenza following contact with an infected person. [press release]. South San Francisco, CA: Genentech; November 23, 2020.

3.    Ikematsu H, Hayden FG, Kawaguchi K, et al. Baloxavir marboxil for prophylaxis against influenza in household contactsN Engl J Med. Published online July 23, 2020. doi: 10.1056/NEJMoa1915341.

This article originally appeared on MPR