Information Baloxavir marboxil Baloxavir marboxil, a cap-endonuclease inhibitor, is an antiviral drug. In vivo Single-dose oral baloxavir marboxil is well tolerated, had a favorable safety profile, and has favorable pharmacokinetic characteristics, including a long half-life, supporting single oral dosing. In nonclinical studies, baloxavir marboxil is a prodrug and is converted to an active form, baloxavir acid, by hydrolysis. After single oral administration in rats and monkeys, plasma concentrations of baloxavir marboxil are below the lower limit of quantification (LLOQ) at all sampling points, and area under the plasma concentration-time curve of baloxavir acid increased dose proportionally. The major excretion route of radioactivity is via fecal excretion, whereas urinary excretion was low in rats and monkeys. Baloxavir marboxil has shown therapeutic activity in preclinical models of influenza A and B virus infections, including strains resistant to current antiviral agents. In murine models of seasonal influenza and avian influenza A(H5N1) or A(H7N9), orally administered baloxavir is associated with rapid reductions in pulmonary viral loads and decreased mortality.