A single-dose tablet for influenza (flu)
Baloxavir marboxil
An antiviral medicine for influenza (flu) that is usually taken as a single dose by mouth.
What is Baloxavir marboxil?
Baloxavir is an antiviral medicine used to treat influenza (flu) in people who would benefit from treatment, and it is unusual in being taken as a single dose by mouth rather than over several days. It works by stopping the flu virus copying itself, which can shorten how long symptoms last if it is started early. It should be swallowed on its own and kept apart from dairy products, antacids and supplements containing minerals such as calcium, iron, magnesium or zinc, which can stop it being absorbed. It treats flu but is not a substitute for the flu vaccine, and the virus can sometimes become less sensitive to it.
Education and reference only. This is a plain-language guide to Baloxavir marboxil — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Baloxavir is an antiviral medicine used to treat influenza, the illness caused by the flu virus, in people who are likely to benefit, such as those at higher risk of complications. Its main feature is that it is usually given as a single dose taken by mouth, rather than a course spread over several days. It is most useful when started soon after symptoms begin. It is an antiviral, meaning it acts against the virus itself rather than just easing symptoms, and it is prescribed under medical guidance.
How it works
The flu virus has to copy its genetic material to multiply and spread inside the body. Baloxavir blocks a step the virus uses to start making new copies of itself, so the amount of virus is reduced and the body can recover sooner. Because it works early in the virus's life cycle, it tends to help most when taken soon after symptoms start. As a single dose, it is convenient, but it works against an infection that is already present rather than preventing flu in the way the vaccine does.
Company & origin
Originated / developed by: Specialist manufacturer.
An antiviral used in the UK to treat influenza (flu), taken as a single dose by mouth.
Practical use
How to take Baloxavir marboxil
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- Take it as the single dose you are prescribed, swallowed by mouth.
- Take it on its own and keep it apart from dairy products such as milk, and from antacids.
- Avoid taking it close to supplements containing calcium, iron, magnesium or zinc, which stop it being absorbed.
- Start it as early as you can after flu symptoms begin, as it works best when taken early.
- Remember it treats flu but does not replace the yearly flu vaccine, which is the main way to prevent flu.
Weighing it up
Advantages & disadvantages of Baloxavir marboxil
Advantages
- Treats influenza and is usually taken as a single, convenient dose by mouth.
- Can shorten how long flu symptoms last when started early.
- Acts against the flu virus itself rather than just easing symptoms.
Disadvantages
- Must be kept apart from dairy, antacids and mineral supplements, which can stop it working.
- Works best only if started soon after symptoms begin.
- The flu virus can sometimes become less sensitive to it, and it does not replace the flu vaccine.
Practical use
Good to know
The most important practical point is how baloxavir is taken: it should be swallowed on its own and kept well apart from dairy products such as milk and from antacids and supplements that contain minerals like calcium, iron, magnesium or zinc, because these bind to it and stop it being absorbed properly. Starting it early, soon after flu symptoms begin, gives the best chance of shortening the illness. It is generally well tolerated, with diarrhoea being one of the more common effects. Two things are worth understanding: the flu virus can sometimes become less sensitive (resistant) to baloxavir, and the medicine treats flu but does not replace the yearly flu vaccine, which remains the main way to prevent flu. Tell your prescriber about your other medicines and supplements so the timing can be sorted out.
Who should not take it / use with caution
- People who have had a serious allergic reaction to baloxavir should not take it.
- It is used with care, and on medical advice, in pregnancy and breastfeeding.
- It should be used under medical guidance, with attention to other medicines and supplements that affect its absorption.
Monitoring
- Reviewing whether symptoms improve after the dose is taken.
- Watching for any allergic-type reaction after taking it.
- Checking other medicines and supplements for timing problems before it is taken.
Side effects
- Diarrhoea, which is one of the more commonly reported effects.
- Headache, nausea or, in some people, bronchitis-type symptoms.
- Rarely, allergic-type reactions, which should be reported promptly.
Key interactions
- Dairy products and antacids bind to baloxavir and reduce how well it is absorbed, so keep them apart.
- Supplements containing calcium, iron, magnesium or zinc also reduce its absorption and should be separated.
- Live flu vaccines may be less effective if given close to it, so tell your prescriber about recent vaccinations.
Available as: Tablets taken by mouth, usually as a single dose.
Answers
Baloxavir marboxil: frequently asked questions
What is baloxavir used for?
It is an antiviral used to treat influenza (flu) in people who would benefit, and it works against the flu virus to help symptoms settle sooner when started early.
Why is it taken as a single dose?
Baloxavir is designed to work after just one dose by mouth, which makes it more convenient than antivirals taken over several days.
Why must I keep it away from milk and supplements?
Dairy, antacids and supplements containing minerals such as calcium, iron, magnesium or zinc bind to baloxavir and stop it being absorbed, so they must be kept apart.
Does it replace the flu jab?
No. Baloxavir treats flu once you have it; the yearly flu vaccine is the main way to prevent flu and is still recommended.
Can the virus stop responding to it?
Yes, the flu virus can sometimes become less sensitive to baloxavir, which is one reason it is prescribed under medical guidance.
The wider class
About Influenza antiviral
Baloxavir marboxil belongs to the influenza antiviral class. For how the class as a whole works, its shared safety principles and monitoring, see the full guide.
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Authoritative sources
- BNF
- NICE CKS
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