Baloxavir (Xofluza) vs oseltamivir (Tamiflu): what the labels say

Both are flu antivirals that the US labels say to start within 48 hours of the first symptoms. They differ in how they work, how you take them, and the ages each label covers. The table is built from the US labels for Xofluza (revised May 2025) and Tamiflu (revised August 2019).

This is general label information, not advice for any one person.

The flu virus needs several of its own enzymes to copy itself and spread. The two drugs block different steps.

Baloxavir marboxil is a prodrug that the body converts to baloxavir. Baloxavir inhibits the endonuclease activity of the viral PA protein, also called the cap-dependent endonuclease. That enzyme is part of the machinery the virus uses to read its genes, so blocking it stops the virus from replicating.

Oseltamivir is a neuraminidase inhibitor. Its active form blocks the enzyme that lets new virus particles leave an infected cell, which limits spread to other cells.

Both labels add that flu viruses change over time, and that the circulating strain and resistance can reduce how much an antiviral helps.

The US Xofluza label covers treatment of uncomplicated flu in people aged 5 and over who have had symptoms for no more than 48 hours, whether healthy or at higher risk of complications. It also covers prevention after contact with someone who has flu, from age 5. It is not indicated under 5 years, because resistant virus was seen more often in that age group in trials.

The US Tamiflu label covers treatment of uncomplicated flu from 2 weeks of age with symptoms for no more than 48 hours, and prevention from 1 year.

Neither label is for other infections, and neither drug has been shown to prevent bacterial complications. If symptoms suggest a bacterial infection on top of flu, see a doctor.

**Baloxavir (Xofluza)** is a single dose taken as soon as possible within 48 hours, for treatment or for prevention after contact. The dose is set by weight (age 5 and over):

For the oral-suspension packets, a 30 mg packet is used at 15 kg to under 20 kg. For the bottle form under 20 kg, the dose is 2 mg per kg.

**Oseltamivir (Tamiflu)**: adults and teenagers aged 13 and over with normal kidney function take 75 mg twice daily for 5 days. For prevention after contact it is 75 mg once daily for at least 10 days, started within 48 hours of contact. Children aged 1 to 12 are dosed by weight (per dose, twice daily for 5 days):

Infants from 2 weeks to under 1 year: 3 mg per kg twice daily. Reduced kidney function means the dose is adjusted using the label's table. These are general summaries. A doctor or pharmacist sets the actual dose.

The label says to avoid it. Baloxavir can bind to calcium, aluminium or magnesium, which may lower the amount of drug in the blood and reduce how well it works. The label says to avoid taking it with:

• dairy products
• calcium-fortified drinks
• laxatives and antacids containing these metal ions
• calcium, iron, magnesium, selenium or zinc supplements

Otherwise Xofluza can be taken with or without food. The Tamiflu label has no similar restriction.

**Baloxavir**: the label lists events in at least 1% of adults and teenagers treated: diarrhoea (3%), bronchitis (3%), nausea (2%), sinusitis (2%) and headache (1%). In children aged 5 to under 12, vomiting and diarrhoea were each reported in 5%. These are trial figures from the label, not a forecast for any individual.

**Oseltamivir**: the label gives nausea, vomiting and headache as the most common effects in treatment studies, and pain as well in prevention studies.

For both, serious allergic reactions have been reported, such as rash, hives and swelling of the face. Stop the drug and get urgent help. Confusion or unusual behaviour has also been reported, especially in children, so watch for it. Neither should be used after a serious allergy to the drug or its ingredients.

No. The Tamiflu label says it is not a substitute for yearly flu vaccination. Both antivirals are for use once someone is ill or has been exposed.

On the nasal-spray live attenuated vaccine, the Tamiflu label says to avoid it from 2 weeks before to 48 hours after Tamiflu unless medically needed. The Xofluza label says the combination has not been evaluated, and that antivirals may reduce how well that vaccine works. For injected vaccines, the Tamiflu label says they can be given at any time, and the Xofluza label says interactions have not been evaluated.

Both labels say there are no adequate, well-controlled studies in pregnant women. Animal studies showed no adverse developmental effects at the exposures tested. Both also note that flu itself puts pregnant women at higher risk of serious complications. On breastfeeding, the Xofluza label says there are no human milk data and that the benefits of breastfeeding should be weighed against the mother's need for the drug.

Anyone pregnant or breastfeeding should ask a doctor before taking either one.

The labels do not rank the two for everyone. The answer depends on age, weight, other conditions, current medicines and supplements, pregnancy, and which flu strains are circulating. That is a decision for a doctor or pharmacist.

• Before starting, if the patient is a child, pregnant or breastfeeding, older, or has a condition such as kidney disease.
• If you take dairy, antacids, or calcium, iron, magnesium, selenium or zinc supplements.
• Severe rash, swollen face, trouble breathing, confusion or unusual behaviour.
• Symptoms get worse after starting, or are no better after several days, which can mean a bacterial infection on top of the flu.