3D model (JSmol)
|Molar mass||157.10 g·mol−1|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Favipiravir, also known as T-705 or Avigan, is an experimental antiviral drug being developed by Toyama Chemical of Japan with activity against many RNA viruses. Like some other experimental antiviral drugs (T-1105 and T-1106), it is a pyrazinecarboxamide derivative. Favipiravir is active against influenza viruses, West Nile virus, yellow fever virus, foot-and-mouth disease virus as well as other flaviviruses, arenaviruses, bunyaviruses and alphaviruses. Activity against enteroviruses  and Rift Valley fever virus has also been demonstrated. Favipiravir showed limited efficacy against Zika virus in animal studies, but was less effective than other antivirals such as MK-608.
The mechanism of its actions is thought to be related to the selective inhibition of viral RNA-dependent RNA polymerase. Other research suggests that favipiravir induces lethal RNA transversion mutations, producing a nonviable viral phenotype. Favipiravir is an orally-administered prodrug and is metabolized to its active form, favipiravir-RTP, following digestion. Human hypoxanthine guanine phosphoribosyltransferase (HGPRT) is believed to play a key role in this activation process. Favipiravir does not inhibit RNA or DNA synthesis in mammalian cells and is not toxic to them.
Ebola virus disease
The drug appears to be effective in a mouse model of Ebola virus disease, but its efficacy against human Ebola infection is unproved. During the 2014 West Africa Ebola virus outbreak, it was reported that a French nurse who contracted Ebola while volunteering for MSF in Liberia recovered after receiving a course of favipiravir. A clinical trial investigating the use of favipiravir against Ebola virus disease was started in Guéckédou, Guinea, during December 2014. Preliminary results showed a decrease in mortality rate in patients with low-to-moderate levels of Ebola virus in the blood, but no effect on patients with high levels of the virus, a group at a higher risk of death. The trial design has been criticised by Scott Hammer and others for using only historical controls. The results of this clinical trial have been presented in February at the annual Conference on Retroviruses and Opportunistic Infections (CROI) 2016 by Daouda Sissoko and published on March 1, 2016 in PLOS Medicine.
- Furuta, Y.; Takahashi, K.; Shiraki, K.; Sakamoto, K.; Smee, D. F.; Barnard, D. L.; Gowen, B. B.; Julander, J. G.; Morrey, J. D. (2009). "T-705 (favipiravir) and related compounds: Novel broad-spectrum inhibitors of RNA viral infections". Antiviral Research. 82 (3): 95–102. doi:10.1016/j.antiviral.2009.02.198. PMID 19428599.
- Furuta, Y.; Gowen, B. B.; Takahashi, K.; Shiraki, K.; Smee, D. F.; Barnard, D. L. (2013). "Favipiravir (T-705), a novel viral RNA polymerase inhibitor". Antiviral Research. 100 (2): 446–54. doi:10.1016/j.antiviral.2013.09.015. PMC . PMID 24084488.
- Caroline AL, Powell DS, Bethel LM, Oury TD, Reed DS; et al. (2014). "Broad Spectrum Antiviral Activity of Favipiravir (T-705) Protection from Highly Lethal Inhalational Rift Valley Fever". PLoS Neglected Tropical Diseases. 8 (4): e2790. doi:10.1371/journal.pntd.0002790.
- Mumtaz N, van Kampen JJ, Reusken CB, Boucher CA, Zika Virus Koopmans MP (2016). "Where Is the Treatment?". Curr Treat Options Infect Dis. 8: 208–211. doi:10.1007/s40506-016-0083-7. PMC . PMID 27547128.
- Jin, Z; Smith, L. K.; Rajwanshi, V. K.; Kim, B; Deval, J (2013). "The ambiguous base-pairing and high substrate efficiency of T-705 (Favipiravir) Ribofuranosyl 5'-triphosphate towards influenza a virus polymerase". PLoS ONE. 8 (7): e68347. doi:10.1371/journal.pone.0068347. PMC . PMID 23874596.
- Baranovich, Tatiana; Wong, Sook-San; Armstrong, Jianling; Marjuki, Henju; Webby, Richard J.; Webster, Robert G.; Govorkova, Elena A. (2013-04-01). "T-705 (favipiravir) induces lethal mutagenesis in influenza A H1N1 viruses in vitro". Journal of Virology. 87 (7): 3741–3751. doi:10.1128/JVI.02346-12. ISSN 1098-5514. PMC . PMID 23325689.
- Smee, Donald F.; Hurst, Brett L.; Egawa, Hiroyuki; Takahashi, Kazumi; Kadota, Takumi; Furuta, Yousuke (2009-07-29). "Intracellular metabolism of favipiravir (T-705) in uninfected and influenza A (H5N1) virus-infected cells". Journal of Antimicrobial Chemotherapy. 64: dkp274. doi:10.1093/jac/dkp274. ISSN 0305-7453. PMC . PMID 19643775.
- Naesens, Lieve; Guddat, Luke W.; Keough, Dianne T.; van Kuilenburg, André B. P.; Meijer, Judith; Vande Voorde, Johan; Balzarini, Jan (2013-10-01). "Role of human hypoxanthine guanine phosphoribosyltransferase in activation of the antiviral agent T-705 (favipiravir)". Molecular Pharmacology. 84 (4): 615–629. doi:10.1124/mol.113.087247. ISSN 1521-0111. PMID 23907213.
- Koons, Cynthia (7 August 2014). "Ebola Drug From Japan May Emerge Among Key Candidates". Bloomberg.com.
- Gatherer D (2014). "The 2014 Ebola virus disease outbreak in West Africa". J. Gen. Virol. 95 (Pt 8): 1619–1624. doi:10.1099/vir.0.067199-0. PMID 24795448.
- Oestereich, L.; Lüdtke, A.; Wurr, S.; Rieger, T.; Muñoz-Fontela, C.; Günther, S. (2014). "Successful treatment of advanced Ebola virus infection with T-705 (favipiravir) in a small animal model". Antiviral Research. 105: 17–21. doi:10.1016/j.antiviral.2014.02.014. PMID 24583123.
- Smither, S. J.; Eastaugh, L. S.; Steward, J. A.; Nelson, M; Lenk, R. P.; Lever, M. S. (2014). "Post-exposure efficacy of oral T-705 (Favipiravir) against inhalational Ebola virus infection in a mouse model". Antiviral Research. 104: 153–5. doi:10.1016/j.antiviral.2014.01.012. PMID 24462697.
- "First French Ebola patient leaves hospital". Reuters. 4 October 2016.
- "Guinea: Clinical Trial for Potential Ebola Treatment Started in MSF Clinic in Guinea". AllAfrica - All the Time. Retrieved 28 December 2014.
- Fink, Sheri (4 February 2015). "Ebola Drug Aids Some in a Study in West Africa". The New York Times.
- Jon Cohen (26 February 2015), "Results from encouraging Ebola trial scrutinized", Science, doi:10.1126/science.aaa7912, retrieved 21 January 2016
- "Favipiravir in Patients with Ebola Virus Disease: Early Results of the JIKI trial in Guinea | CROI Conference". www.croiconference.org. Retrieved 2016-03-17.
- Sissoko, Daouda; Laouenan, Cedric; Folkesson, Elin; M’Lebing, Abdoul-Bing; Beavogui, Abdoul-Habib; Baize, Sylvain; Camara, Alseny-Modet; Maes, Piet; Shepherd, Susan. "Experimental Treatment with Favipiravir for Ebola Virus Disease (the JIKI Trial): A Historically Controlled, Single-Arm Proof-of-Concept Trial in Guinea". PLOS Medicine. 13 (3): e1001967. doi:10.1371/journal.pmed.1001967. PMC . PMID 26930627.