Treating Influenza with Baloxavir (Xofluza)

The Full Story

During the SARS-CoV-2 (COVID-19) pandemic, viruses have been in the news a lot. Now, influenza season is upon us again. Flu shots are currently available to protect against the strains of influenza A and B expected to predominate during the 2021–2022 season. If you haven’t gotten a flu shot yet, do it now! Flu season peaks from December through February but can continue as late as May. This year, people can get a COVID vaccine at the same time as their flu shot. The US Centers for Disease Control and Prevention (CDC) predicts that since much less seasonal flu activity was seen last winter because of the COVID-19 pandemic, people might have lower immunity, resulting in a more severe flu season this year.

Influenza costs the US well over $10 billion annually for hospitalizations and outpatient care. Getting vaccinated reduces a person’s risk of getting the flu by 40 to 60%. If someone does come down with influenza A or B, an antiviral medication might be prescribed. Baloxavir marboxil (Xofluza) and oseltamivir (Tamiflu) are the two main oral antivirals for preventing and treating the flu. Baloxavir became available more recently and it works differently than oseltamivir (Tamiflu) and the other flu antivirals. Because of this, baloxavir might be active against some strains of flu that are resistant to oseltamivir.

Baloxavir is FDA-approved to treat the flu in people 12 years of age and older who are otherwise healthy. It must be started within 48 hours after flu symptoms appear. Baloxavir has been shown to shorten the duration of the illness by about 1 day, compared with placebo. This is similar to the treatment effectiveness of oseltamivir. However, oseltamivir is currently preferred over baloxavir to treat influenza in patients who are hospitalized, have severe symptoms, or are at increased risk for complications (e.g., children under 5 years old, adults 65 years and older, pregnant women, residents of chronic care facilities like nursing homes, and people who are immunosuppressed or have chronic health conditions like asthma and diabetes). 

If a person is at high risk for complications, baloxavir can also be used to help prevent flu from developing after exposure to someone with influenza within the preceding 48 hours. This is known as post-exposure prophylaxis (PEP). Oseltamivir is also approved to prevent influenza in these high-risk patients.

None of the antivirals that are FDA-approved for influenza have been found to be effective for treating COVID-19.

Depending on a person’s weight, the dosage of baloxavir is one or two 40-mg tablets, taken once. The medication stays active for a long time, and additional doses are not necessary. It takes about 2 weeks for the drug to be completely eliminated from the body. Overdoses with baloxavir have not been reported so far. This is likely because the medication is available only in single-dose blister packages.

When side effects occur, they tend to be mild and infrequent. Only 3% or less of patients report diarrhea, nausea, vomiting, or headache after taking baloxavir. The drug appears to cause less nausea and vomiting than oseltamivir.

Something to be cautious about is that calcium, magnesium, and aluminum in the diet will bind with baloxavir and reduce its absorption into the body. These minerals occur in dairy products, antacids, and dietary supplements. Don’t take baloxavir at the same time as any of these. However, someone who unintentionally gets a dose of baloxavir might counteract it by taking a dose of an antacid containing calcium or magnesium.

Baloxavir has several similarities and differences when compared to oseltamivir:

• Both drugs are approved for the prevention and treatment of influenza A and B.
• Baloxavir is not FDA-approved for children under 12 years of age. Oseltamivir is approved for patients 2 weeks of age and older.
• Baloxavir is given as a single dose, while oseltamivir requires 5 days of treatment.
• Either medication should be started within 48 hours of symptom appearance or exposure to someone with the flu.
• Oseltamivir is preferred over baloxavir for patients who are pregnant, hospitalized, or have severe or complicated influenza.
• Baloxavir leads to slightly faster symptom improvement than oseltamivir (see “This Really Happened”), and might be more effective against influenza B.
• Minerals such as calcium, magnesium, and aluminum can bind with baloxavir and reduce its absorption, so do not take antacids, dairy products, or supplements with baloxavir. Oseltamivir does not interact with commonly used medications.
• Side effects of baloxavir are mild and infrequent (diarrhea 3%, headache 1%, and nausea 1%). It causes less nausea and vomiting than oseltamivir.
• Baloxavir is about twice as expensive as generic oseltamivir.

If someone has unintentionally taken a dose of baloxavir, go to webPOISONCONTROL® for help online or call Poison Control at 1-800-222-1222. Whether you log on or call, expert assistance is available 24 hours a day. Both options are free for the public, and available 24 hours a day.

Leslie A. McCament-Mann, PhD, RPh
Clinical Toxicologist