Baloxavir

Baloxavir is a drug employed in the treatment of influenza virus infection.
Baloxavir marboxil is a selective inhibitor of influenza cap-dependent endonuclease. It has shown therapeutic activity in preclinical models of influenza A and B virus infections, including strains resistant to current antiviral agents.

Baloxavir is a prodrug of baloxavir acid that selectively inhibits the cap-dependent endonuclease of the polymerase acidic subunit of the viral polymerase, offering clinical advantages such as a single-dose regimen and rapid viral clearance[1][2]. Baloxavir increases the model-based estimated viral clearance rate by 86% in patients with acute influenza and achieves a median viral clearance half-life of 5.7 hours[1]. Single-dose baloxavir provides an operational advantage owing to the long half-life of baloxavir acid, although its application carries the risk of selecting and spreading drug-resistant mutants[1].

Baloxavir is a drug employed in the treatment of influenza virus infection.

Baloxavir marboxil is an influenza therapeutic agent, specifically, an enzyme inhibitor targeting the influenza virus' cap-dependent endonuclease activity, one of the activities of the virus polymerase complex. In particular, it inhibits a process known as cap snatching, by which the virus derives short, capped primers from host cell RNA transcripts, which it then uses for polymerase-catalyzed synthesis of its needed viral mRNAs. A polymerase subunit binds to the host pre-mRNAs at their 5' caps, then the polymerase's endonuclease activity catalyzes its cleavage "after 10–13 nucleotides". As such, its mechanism is distinct from neuraminidase inhibitors such as oseltamivir and zanamivir.

Common side effects following the single dose administration of baloxavir marboxil include diarrhea, bronchitis, common cold, headache, and nausea. Adverse events were reported in 21% of people who received baloxavir, 25% of those receiving placebo, and 25% of oseltamivir.

[1] Jittamala, P., Schilling, W. H. K., Leopold, S. J., Watson, J. A., Kotchum, K., Wongnak, P., Seers, T., Asawasriworanan, T., Singh, S., Beer, E., Ngernseng, T., Suwannasin, K., Madmanee, W., Phommasone, K., Shrestha, S., de Aguiar, R. S., Batty, E. M., Teixeira, M. M., Karkey, A., … White, N. J. (2026). Baloxavir marboxil, favipiravir, or oseltamivir in patients with non-severe symptomatic seasonal influenza (AD ASTRA): a phase 2, open-label, adaptive, randomised controlled trial. Lancet Infectious Diseases. https://doi.org/10.1016/S1473-3099(26)00255-0
[2] Zhan, P., Ren, Y., Han, K., Jin, G., Yang, Y., Shi, L., & Ci, Y. (2026). Baloxavir Acid-Induced Mitochondrial Toxicity and Cell Cycle Arrest Contribute to Its Adverse Effects. International Journal of Molecular Sciences, 27 7. https://doi.org/10.3390/ijms27072967