This study explains that the Seasonal influenza, an acute respiratory infectious disease caused by influenza viruses, spreads easily from person to person and causes seasonal epidemics worldwide.1-4 Although influenza vaccination is the most effective way to prevent the disease, epidemics continue to occur, indicating the need for anti-influenza drugs to control influenza virus infection.5, 6 Currently, neuraminidase inhibitors (NAIs), including oseltamivir phosphate (OSP), are the most widely used class of anti-influenza drugs. Baloxavir marboxil (BXM), and its active form baloxavir acid (BXA), is a first-in-class, small-molecule inhibitor of cap-dependent endonuclease (CEN),9 which has been approved for clinical use (single dose of 40 mg for patients 40 to <80 kg or 80 mg for patients ≥80 kg) in uncomplicated adults and adolescents in Japan and the United States for the treatment of influenza type A and B virus infections. The CEN in the polymerase acidic protein (PA), a subunit of influenza virus polymerase, mediates the cap-snatching process during viral mRNA biosynthesis.10, 11 BXA exhibits broad-spectrum inhibitory activity against seasonal, avian and swine influenza viruses including NAI-resistant strains in vitro and in vivo. A previous phase 1 trial revealed that a single oral dose of BXM from 6 to 80 mg was rapidly metabolized to BXA, and the terminal elimination half-life of BXA ranged from 49 to 91 hours.

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