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Food and Drug Administration (FDA) approves baloxavir marboxil (XOFLUZATM): first new flu drug in 20 years

By: Ruchira Kasbekar, PharmD Candidate c/o 2020

It is estimated that approximately 80,000 Americans died from the flu during the 2017-2018 flu season which is the highest death toll from influenza in the last four decades.1 As the 2017-2018 flu season progressed, there was a shortage of oseltamivir (Tamiflu®) availability. To prevent shortages during the 2018-2019 flu season, the Food and Drug Administration (FDA) approved baloxavir marboxil (XOFLUZA™) in October of 2018 for the treatment of acute uncomplicated influenza in patients 12 years of age and older who have been symptomatic for no more than 48 hours.2 The approval was granted to Japanese pharmaceutical company Shionogi and Co., and the drug will be distributed throughout the United States by Genentech, an American biotechnology company based in San Francisco, California.2

Baloxavir marboxil (oxymethyl methylcarbamate) is a polymerase acidic endonuclease inhibitor and is the first influenza treatment to be approved by the FDA in twenty years.3 It is a prodrug which is converted via hydrolysis to free baloxavir that is the influenza virus antagonist. Endonuclease is an influenza virus specific enzyme in RNA polymerase complex which is used in gene transcription. Baloxavir marboxil is active against influenza strains A/H1N1 and A/H5N1, viruses with the neuraminidase (NA) substitution H275Y, A/H3N2 virus with the NA substitution E119V, A/H7N9 virus with the NA substitution R292K, and type B virus with NA substitution D198E.2 Additionally, in research conducted to test the novel drug’s cross resistance with other classes of anti-influenza medications, it was found that baloxavir marboxil and neuraminidase inhibitors target different viral proteins. 

Two clinical trials were conducted by Shionogi and Co., and Genentech to ensure the drug’s safety and efficacy before it was approved.3 In both trials, baloxavir marboxil was recommended for its ability to shorten the time needed to relieve influenza symptoms. The first clinical trial was a placebo-controlled phase 2 dose finding trial. It included 400 adults between the ages of 20 to 64 with the average age being 38 years old. Sixty three percent of the patients enrolled in the trial who received baloxavir marboxil had influenza A/H1N1, twenty five percent of the patients had influenza B, and less than fifteen percent of enrolled patients had influenza A/H3N2. The estimated time needed to relieve symptoms in influenza B patients taking baloxavir marboxil 40 mg was 63 hours (95% CI of 43, 70), while subjects receiving the placebo experienced complete symptomatic relief after 83 hours (95% CI of 58, 93).4

The second clinical trial was a phase 3 active and placebo-controlled trial. This trial examined patients which contracted the A/H3N2 strain of influenza. One thousand four hundred and thirty-six adults and adolescents between the ages of 12 to 64 were enrolled in the study. Patients that were between the ages of 20 to 64 were administered baloxavir marboxil, the placebo single oral dose on Day 1, or oseltamivir twice a day for five days. Adolescents between the ages of 12 to 20 received baloxavir marboxil or the placebo as a single oral dose. The results of the trial found that there is no difference between oseltamivir and baloxavir marboxil in terms of the time needed to alleviate influenza symptoms. For subjects between the ages of 12 and 17, the median time needed for complete symptomatic relief after having received baloxavir marboxil was 54 hours (95% CI of 43, 81) compared to 93 hours (95% CI of 64, 118) after having received the placebo. 4

Baloxavir marboxil is to be administered as a single dose oral formulation against both influenza A and B.4 It has not shown to be effective in children under the age of 12 as well as individuals weighing less than 88 pounds. Symptoms are seen to reduce significantly within two days of administration and the drug can be taken with or without food. Patients should be advised to not take baloxavir marboxil with dairy products, polyvalent cation containing laxatives, antacids, and dietary supplements. Co-administration with these products may decrease the plasma concentration and reduce the efficacy of baloxavir marboxil. Common side effects of baloxavir marboxil include mild symptoms such as diarrhea and bronchitis.4 

Baloxavir marboxil offers a single dose regimen compared to other flu medications, such as oseltamivir, which provide multi-day dosing regimens. This is a huge benefit to many patients since adherence and convenience are major issues for people of all ages who are taking medications. As new drugs come onto the market, pharmacists have the responsibility to make their patients aware of newly available therapeutic options as well as ensure that compliance is maintained with all their medication regimens.


  1. McNeil D. F.D.A. Approves New Drug for Flu. The New York Times. https://www.nytimes.com/2018/10/24/health/flu-pill-xofluza.html. Published 10/24/2018.
  2. Hunt A. FDA approves new drug to treat influenza. US Food and Drug Administration Home Page. https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm624226.htm. Published 10/24/2018.
  3. FDA approves first new influenza treatment in two decades. Pharmaceutical Technology. https://www.pharmaceutical-technology.com/news/fda-approves-influenza-drug-xofluza/. Published 10/25/2018.
  4. XOFLUZA (baloxavir marboxil) [package insert]. USA; Genentech; Revised 10/31/2018.
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