Pyrazine derivatives such as T-705, 3-hydroxypyrazine-2-carboxamide (T-1105), and 3,4-dihydro-3-oxo-4-β-d-ribofuranosyl-2-pyrazinecarboxamide (T-1106), blocks the replication of many RNA viruses, including arenaviruses (Junin, Machupo, and Pichinde), and are expected to be an effective antiviral drug for COVID-19. The selective inhibition of viral RNA-dependent RNA polymerase (RdRp) is assumed to be the mechanism of action for their anti-SARS-CoV-by their analog effect but cannot kill the virus. Therefore, the immune response must be used to kill the virus while also preventing it from multiplying. Considering these biological conditions for its mechanism of action in vivo, the effective concentration of its active form after the metabolization will be lower, although T-705 is available in both oral and intravenous formulations. Regarding the favipiravir as a prodrug of the RNA polymerase inhibitor, the purpose is to supply favipiravir-RTP; the active form is a purine nucleic acid analog vicinity of the virus in inflamed organs such as the lung. However, if most of the dosed T-705 is decomposed during the conversion processes to the active form and drug delivery, the concentration near the virus drops to a level where the desired antiviral effect cannot be obtained.