baloxavir marboxil
Baloxavir marboxil (Xofluza) is an oral antiviral used to treat acute uncomplicated influenza in patients 5 years of age and older and for post-exposure prophylaxis in that age group. It blocks the influenza virus's cap-snatching enzyme (PA endonuclease), stopping the virus from making the mRNA it needs to replicate. It is taken as a single oral dose for treatment.
This page is based on FDA prescribing information for Xofluza, cross-checked with MedlinePlus and the National Cancer Institute drug dictionary; the mechanism is explained in plain language, and analogies are used only where they stay accurate.
How it works
Explains what the medicine does in the body, not dosing, side effects, or safety.
An analogy
Flu viruses are like counterfeiters that steal the 'official stamps' (caps) from the host cell's own documents so their fake documents look real. Baloxavir breaks the virus's stamp-stealing tool (PA endonuclease). Without stolen caps, the virus cannot produce the readable instructions it needs to make more copies of itself, and the infection stalls.
In simple terms
Baloxavir marboxil is an antiviral medicine that treats and prevents the flu. It works by blocking an enzyme inside the flu virus called PA endonuclease. This enzyme is part of the virus's cap-snatching system: it cuts off the caps from the host cell's own RNA and uses them to start making viral RNA. When baloxavir blocks this enzyme, the virus can no longer make the RNA instructions it needs to replicate. Baloxavir is taken by mouth, usually as a single dose for treatment, and it helps shorten flu symptoms. It does not prevent bacterial infections that may occur as a complication of the flu.
In depth
Baloxavir marboxil is an orally bioavailable prodrug that is converted by hydrolysis to its active metabolite baloxavir. Baloxavir targets, binds to, and inhibits the cap-dependent endonuclease (CEN) activity of the influenza polymerase acidic (PA) protein, an influenza virus-specific enzyme in the viral RNA polymerase complex required for initiation of influenza gene transcription. By inhibiting PA endonuclease, baloxavir blocks cap-snatching and halts influenza viral mRNA replication, reducing viral load and preventing further influenza infection. It is indicated for treatment of acute uncomplicated influenza in patients 5 years of age and older who have been symptomatic for no more than 48 hours, and for post-exposure prophylaxis of influenza in persons 5 years of age and older following contact with an individual who has influenza.
See it in motion
A schematic animation of the mechanism — simplified for clarity, not drawn to scale.
Flu viruses are like counterfeiters that steal the 'official stamps' (caps)
- Baloxavir marboxil is an antiviral medicine that treats and prevents the flu.
- It works by blocking an enzyme inside the flu virus called PA endonuclease.
- This enzyme is part of the virus's cap-snatching system: it cuts off the caps from the host cell's own RNA and uses them to start making viral RNA.
- Without stolen caps, the virus cannot produce the readable instructions it needs to make more copies of itself, and the infection stalls.
Target: Influenza polymerase acidic (PA) endonuclease
Baloxavir's active metabolite inhibits the cap-dependent endonuclease activity of the influenza PA protein, an enzyme in the viral RNA polymerase complex required for initiation of viral gene transcription.
Approved uses
Approved uses differ by country and change over time. Always follow your local prescribing information.
Approved uses in United States
FDA- Treatment of acute uncomplicated influenza in patients 5 years of age and older who have been symptomatic for no more than 48 hours and who are otherwise healthy or at high risk of developing influenza-related complications
- Post-exposure prophylaxis of influenza in patients 5 years of age and older following contact with an individual who has influenza
Approved uses in United States
MedlinePlus- Treatment and prevention of influenza in certain circumstances
Approved uses in United States
NCI- Inhibition of influenza cap-dependent endonuclease, halting viral mRNA replication and reducing viral load
Official sources
The statements on this page trace back to these records.
- U.S. Food and Drug Administration: Xofluza prescribing information
U.S. Food and Drug Administration
- MedlinePlus: baloxavir marboxil
MedlinePlus, U.S. National Library of Medicine
- National Cancer Institute: baloxavir marboxil
National Cancer Institute
This page explains how the medicine works — it isn’t the patient leaflet. For anything that applies to you, read the leaflet that came with your medicine or ask your pharmacist.
MedUnfold provides educational content and is not medical advice. Always follow your local prescribing information and healthcare professional.