Intracellular metabolism of favipiravir (T-705) in uninfected and influenza A (H5N1) virus-infected cells

J Antimicrob Chemother. 2009 Oct;64(4):741-6. doi: 10.1093/jac/dkp274. Epub 2009 Jul 29.


Objectives: To determine the metabolism of favipiravir (T-705, 6-fluoro-3-hydroxy-2-pyrazinecarboxamide) to its ribosylated, triphosphorylated form (T-705 RTP) in uninfected and influenza A/Duck/MN/1525/81 (H5N1) virus-infected cells. Effects of treatment on intracellular guanosine triphosphate (GTP) pools and influenza virus-inhibitory activity were also assessed.

Methods: A strong anion exchange HPLC separation method with UV detection was used to quantify T-705 RTP and GTP levels in Madin-Darby canine kidney cells. Antiviral activity was determined by virus yield reduction assay.

Results: Accumulation of T-705 RTP in uninfected cells increased linearly from 3 to 320 pmol/10(6) cells in cells exposed to 1-1000 microM extracellular T-705 for 24 h, approaching maximum levels by 9 h. Virus infection did not result in greater T-705 RTP accumulation compared with uninfected cells. Catabolism of T-705 RTP occurred after removal of T-705 from the extracellular medium, with a half-life of decay of 5.6 +/- 0.6 h. Based upon these results, short-term incubation of T-705 with H5N1 virus-infected cells was predicted to provide an antiviral benefit. Indeed, 4-8 h 10-100 microM T-705 treatment of cells resulted in virus yield reductions, but less than continuous exposure. A 100-fold higher extracellular concentration of T-705 was required to inhibit intracellular GTP levels compared with ribavirin, which helps explain ribavirin's greater toxicity.

Conclusions: The favourable intracellular metabolic properties of T-705 combined with its reduced cell-inhibitory properties make this compound an attractive candidate for treating human influenza virus infections.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amides / metabolism*
  • Amides / pharmacology*
  • Animals
  • Antiviral Agents / metabolism*
  • Antiviral Agents / pharmacology*
  • Cell Line
  • Chromatography, High Pressure Liquid / methods
  • Cytosol / chemistry
  • Dogs
  • Guanosine Triphosphate / analysis
  • Influenza A Virus, H5N1 Subtype / drug effects*
  • Influenza A Virus, H5N1 Subtype / growth & development*
  • Pyrazines / metabolism*
  • Pyrazines / pharmacology*
  • Spectrophotometry, Ultraviolet / methods


  • Amides
  • Antiviral Agents
  • Pyrazines
  • Guanosine Triphosphate
  • favipiravir