Toshihiko Sugiki, Akihiro Ito, Yuko Hatanaka, Masaki Tsukamoto, Tsuyoshi Murata, Koichiro Miyanishi, Akinori Kagawa, Toshimichi Fujiwara, Masahiro Kitagawa, Yasushi Morita, and Makoto Negoro
Favipiravir (brand name Avigan), a widely known anti-influenza prodrug, is metabolized by endogenous enzymes of host cells to generate the active form, which exerts inhibition of viral RNA-dependent RNA polymerase activity; first, favipiravir is converted to its phosphoribosylated form, favipiravir-ribofuranosyl-5'-monophosphate (favipiravir-RMP), by hypoxanthine-guanine phosphoribosyltransferase (HGPRT). Because this phosphoribosylation reaction is the rate-determining step in the generation of the active metabolite, quantitative and real-time monitoring of the HGPRT-catalyzed reaction is essential to understanding the pharmacokinetics of favipiravir. However, assay methods enabling such monitoring have not been established.