Baloxavir marboxil

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Baloxavir marboxil
Baloxavir marboxil.svg
Clinical data
Trade namesXofluza
Other namesBXM (S-033188)
BXA (S-033447)
License data
  • US: N (Not classified yet) [1]
Routes of
By mouth
ATC code
Legal status
Legal status
CAS Number
PubChem CID
Chemical and physical data
Molar mass571.55 g·mol−1
3D model (JSmol)

Baloxavir marboxil, sold under the brand name Xofluza, is an antiviral medication for treatment of influenza A and influenza B flu.[2] It was approved for medical use in Japan and in the United States[3] in 2018, and is taken as a single dose by mouth.[2] It may reduce the duration of flu symptoms by about a day, but is prone to selection of resistant mutants that render it ineffectual.[medical citation needed]

Baloxavir marboxil (BXM) was developed as a prodrug strategy, with its metabolism releasing the active agent, baloxavir acid (BXA). BXA then functions as enzyme inhibitor, targeting the influenza virus' cap-dependent endonuclease activity, used in "cap snatching" by the virus' polymerase complex, a process essential to its life-cycle.[4]

BXM was developed for the market by Shionogi Co., a Japanese pharmaceutical company, and Switzerland-based Roche AG.[5] The names under which BXM and BXA appear in Shionogi research reporting are S-033188 and S-033447, respectively.

Medical use[edit]

Baloxavir marboxil, sold under the trade name "Xofluza", is an influenza medication, an antiviral,[6][2] that is taken as a single dose tablet,[6] by mouth, by individuals that are 12 years of age or older,[6] that have presented symptoms of this infection for no more than 48 hours.[6][7] The efficacy of baloxavir marboxil administered after 48 hours has not been tested.[6]


In 2.2% of baloxavir recipients in the Phase II trial and in about 10% of baloxavir recipients in the Phase III trial, the infecting influenza strain had acquired resistance to the drug, due to variants of the polymerase protein displaying substitutions of isoleucine-38, specifically, the I38T, I38M, or I38F mutations.[8] There is continuing research into and clinical concern over the resistance appearing in patients, in response to treatment with this drug.[9][10][11]

Side effects[edit]

Common side effects following the single dose administration of baloxavir were diarrhea, bronchitis, common cold, headache, and nausea.[2][7][3] Adverse events were reported in 21% of people who received baloxavir, 25% of those receiving placebo, and 25% of oseltamivir.[8]

Mechanism of action[edit]

Baloxavir marboxil is an influenza therapeutic agent, specifically, an enzyme inhibitor targeting the influenza virus' cap-dependent endonuclease activity, one of the activities of the virus polymerase complex.[12] In particular, it inhibits a process known as cap snatching,[citation needed] by which the virus derives short, capped primers from host cell RNA transcripts, which it then uses for polymerase-catalyzed synthesis of its needed viral mRNAs.[13][non-primary source needed] A polymerase subunit binds to the host pre-mRNAs at their 5′-caps, then the polymerase's endonuclease activity catalyzes its cleavage "after 10–13 nucleotides".[13][non-primary source needed] As such, its mechanism is distinct from neuraminidase inhibitors such as oseltamivir and zanamivir.[citation needed]


Baloxavir marboxil is a substituted pyridone derivative of a polycyclic family, whose chemical synthesis has been reported in a number of ways by the company discovering it, Shionogi and Co. of Japan (as well as others); the Shinogi reports have appeared several times in the Japanese patent literature between 2016 and 2019, providing insight into possible industrial synthetic routes that may be in use.[14][better source needed][15][16][17][18][19]

Baloxavir marboxil (BXM) is a prodrug whose active agent, baloxavir acid (BXA) is released rapidly in vivo, as the hydrolysis of BXM is catalysed by arylacetamide deacetylases in cells of the blood, liver, and lumen of the small intestine.[20][21][22] The compound numbers for BXM and BXA used in publications by Shionogi and others during discovery and development (prior to assignment of a USAN name) were, respectively, S-033188 and S-033447.[23] As reported in a review of the patent literature, the carbonic acid ester (carbonate) moiety of the prodrug—shown in the lower left-hand corner of the image above—was prepared during discovery and development research from a late stage 2-hydroxy-4-pyridone precursor by treatment with chloromethyl methyl carbonate.[20][24]


Japan's Ministry of Health, Labour and Welfare (JMHLW) and the U.S. Food and Drug Administration (FDA) approved baloxavir marboxil based on evidence of its benefits and side effects from two clinical trials in adult and pediatric patients with uncomplicated influenza (Trial 1, 1518T0821 and Trial 2, NCT02954354[25]),[2] involving 1119 patients.[7][26][better source needed][verification needed] Both trials included clincal sites and patients in Japan, with Trial 2 adding clinical locations in the United States.[7][2]

As of September 2018, in the only report of a Phase III randomized, controlled trial, baloxavir reduced the duration of influenza symptoms of otherwise healthy outpatients by about one day compared to a placebo treatment group, and comparable to what was seen for a oseltamivir treatment group.[7] On the first day after baloxavir was started in its treatment group of patients, viral loads decreased more than in patients in either the oseltamivir or placebo groups; however, after five days, the effect on viral load of the single dose of baloxavir was indistinguishable from the effect observed following the complete, 5-day regimen of oseltamivir in its treatment group.[8][verification needed]

Baloxavir marboxil was approved for sale in Japan in February 2018.[27][better source needed] On 24 October 2018, the FDA approved it for the treatment of acute uncomplicated influenza in people 12 years of age and older who have been symptomatic for no more than 48 hours.[3] The FDA application of baloxavir marboxil was granted priority review in the United States, and approval of Xofluza was granted to Shionogi & Co., Ltd. in October 2019.[3] Specifically, the FDA approved the use of baloxavir marboxil for people at high risk of developing influenza-related complications.[28]


  1. ^ "Baloxavir marboxil (Xofluza) Use During Pregnancy". 14 November 2018. Retrieved 9 January 2020.
  2. ^ a b c d e f "Xofluza- baloxavir marboxil tablet, film coated". DailyMed. 28 October 2019. Retrieved 9 January 2020.
  3. ^ a b c d "FDA approves new drug to treat influenza". U.S. Food and Drug Administration (FDA) (Press release). 24 October 2018. Archived from the original on 24 October 2019. Retrieved 23 October 2019. This article incorporates text from this source, which is in the public domain.
  4. ^ Noshi T, Kitano M, Taniguchi K, et al. (December 2018). "In vitro characterization of baloxavir acid, a first-in-class cap-dependent endonuclease inhibitor of the influenza virus polymerase PA subunit". Antiviral Res. 160: 109–117. doi:10.1016/j.antiviral.2018.10.008. PMID 30316915.
  5. ^ Branswell, Helen (27 June 2018). "A flu drug — shown to reduce the duration of symptoms — could upend treatment in U.S.". Stat.
  6. ^ a b c d e "Baloxavir Marboxil Monograph for Professionals". American Society of Health-System Pharmacists. 19 August 2019. Retrieved 9 January 2020.
  7. ^ a b c d e Food and Drug Administration (23 July 2019). "Drug Trial Snapshot: Xofluza". U.S. Food and Drug Administration (FDA). Retrieved 7 January 2020. This article incorporates text from this source, which is in the public domain.
  8. ^ a b c Hayden FG, Sugaya N, Hirotsu N, et al. (September 2018). "Baloxavir Marboxil for Uncomplicated Influenza in Adults and Adolescents". N. Engl. J. Med. 379 (10): 913–923. doi:10.1056/NEJMoa1716197. PMID 30184455.
  9. ^ "Roche's flu med Xofluza drives drug resistance and may be a bad choice for kids, study says". FiercePharma.
  10. ^ "New flu drug drives drug resistance in influenza viruses". EurekAlert!.
  11. ^ Imai M, Yamashita M, Sakai-Tagawa Y, et al. (January 2020). "Influenza A variants with reduced susceptibility to baloxavir isolated from Japanese patients are fit and transmit through respiratory droplets". Nature Microbiology. 5 (1): 27–33. doi:10.1038/s41564-019-0609-0. PMID 31768027.
  12. ^ Eisfeld, Amie J.; Neumann, Gabriele; Kawaoka, Yoshihiro (8 January 2015). "At the centre: influenza A virus ribonucleoproteins". Nature Reviews. Microbiology. 13 (1): 28–41. doi:10.1038/nrmicro3367. PMC 5619696. PMID 25417656.
  13. ^ a b Dias A, Bouvier D, Crépin T, et al. (April 2009). "The cap-snatching endonuclease of influenza virus polymerase resides in the PA subunit". Nature. 458 (7240): 914–8. Bibcode:2009Natur.458..914D. doi:10.1038/nature07745. PMID 19194459.
  14. ^ MedKoo Staff (8 January 2020). "Baloxavir marboxil: Synthetic Routes [Five Tabs]". Morrisville, NC: MedKoo Biosciences. Retrieved 8 January 2020.
  15. ^ Okamoto, Kazuya; Ueno, Tatsuhiko; Hato, Yoshio; Hakogi, Toshikazu; Majima, Shohei. Method for stereoselective preparation of substituted polycyclic pyridone derivative. Assignee Shionogi & Co., Ltd., Japan. WO 2019070059. (2019).
  16. ^ Kawai, Makoto; Tomita, Kenji; Akiyama, Toshiyuki; Okano, Azusa; Miyagawa, Masayoshi. Pharmaceutical composition containing polycyclic pyridone derivatives as cap-dependent endonuclease (CEN) inhibitors. Assignee Shionogi and Co., Ltd., Japan. JP 6249434. (2017).
  17. ^ Shibahara, Setsuya; Fukui, Nobuaki; Maki, Toshikatsu. Polycyclic pyridone derivative, crystal and preparation method thereof. Assignee Shionogi and Co., Ltd., Japan. JP 6212678. (2017).
  18. ^ Kawai, Makoto; Tomita, Kenji; Akiyama, Toshiyuki; Okano, Azusa; Miyagawa, Masayoshi. Preparation of polycyclic pyridone derivatives as cap-dependent endonuclease (CEN) inhibitors and prodrugs thereof. Assignee Shionogi and Co., Ltd., Japan. JP 5971830. (2016).
  19. ^ See also: Zhu, Xiaoyun; Jiang, Weiping. Process for preparation of substituted polycyclic carbamoylpyridone derivative and its prodrug. CN 108440564. (2018).
  20. ^ a b Hughes, David L. (21 June 2019). "Review of the Patent Literature: Synthesis and Final Forms of Antiviral Drugs Tecovirimat and Baloxavir Marboxil". Organic Process Research & Development. 23 (7): 1298–1307. doi:10.1021/acs.oprd.9b00144.
  21. ^ Yoshino, Ryunosuke; Yasuo, Nobuaki; Sekijima, Masakazu (25 November 2019). "Molecular Dynamics Simulation reveals the mechanism by which the Influenza Cap-dependent Endonuclease acquires resistance against Baloxavir marboxil". Scientific Reports. 9 (1): 17464. Bibcode:2019NatSR...917464Y. doi:10.1038/s41598-019-53945-1.
  22. ^ Kawaguchi, Nao; Koshimichi, Hiroki; Ishibashi, Toru; Wajima, Toshihiro (1 November 2018). "Evaluation of Drug–Drug Interaction Potential between Baloxavir Marboxil and Oseltamivir in Healthy Subjects". Clinical Drug Investigation. 38 (11): 1053–1060. doi:10.1007/s40261-018-0697-2.
  23. ^ Yang, Jie; Huang, Yingna; Liu, Shuwen (4 May 2019). "Investigational antiviral therapies for the treatment of influenza". Expert Opinion on Investigational Drugs. 28 (5): 481–488. doi:10.1080/13543784.2019.1606210. PMID 31018720.
  24. ^ "Baloxavir Marboxil". Pharmaceutical Substances.
  25. ^ Clinical trial number NCT02954354 for "A Study of S-033188 (Baloxavir Marboxil) Compared With Placebo or Oseltamivir in Otherwise Healthy Patients With Influenza (CAPSTONE 1)" at
  26. ^ Otake, Tomoko (24 February 2018). "One-dose flu drug Xofluza gets nod from health ministry". Japan Times Online.
  27. ^ "Xofluza (Baloxavir Marboxil) Tablets 10mg/20mg Approved For The Treatment Of Influenza Types A And B In Japan" (Press release). Shionogi & Co., Ltd. 23 February 2018 – via
  28. ^ "Genentech Announces FDA Approval of Xofluza (Baloxavir Marboxil) for People at High Risk of Developing Influenza-Related Complications" (Press release). Genentech. 17 October 2019. Archived from the original on 24 October 2019. Retrieved 23 October 2019 – via Business Wire.

Further reading[edit]

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