Baloxavir marboxil (Xofluza)

How Medicare covers it

Part D (forms used at home). Part A during a covered inpatient stay. No Part B clinician-administered form in the CMS Part B spending file.

What it treats

Treats acute uncomplicated influenza (the flu) in patients 5 years of age and older who have had symptoms for no more than 48 hours and who are otherwise healthy or at high risk of flu complications. It is also used to prevent the flu in persons 5 years of age and older after contact with someone who has the flu (post-exposure prophylaxis).

What it is for, in depth

Baloxavir marboxil treats acute uncomplicated influenza, the flu, and it is also used to prevent the flu after contact with someone who has the flu, called post-exposure prophylaxis. For treatment, it is for patients 5 years of age and older who have had symptoms for no more than 48 hours and who are otherwise healthy or at high risk of flu complications. For prevention, it is for persons 5 years of age and older after contact with someone who has the flu. Timing is a key part of where it fits: treatment is taken as soon as possible after symptoms start. It works as an influenza virus polymerase acidic endonuclease inhibitor, blocking an enzyme the flu virus needs to copy itself, which stops the virus from spreading in the body. It comes as baloxavir marboxil 40 MG Oral Tablet [Xofluza] and baloxavir marboxil 80 MG Oral Tablet [Xofluza], taken by mouth as a single one-time dose based on weight.

How it works

It is an influenza virus polymerase acidic (PA) endonuclease inhibitor. It blocks an enzyme the flu virus needs to copy itself, which stops the virus from spreading in the body.

How it is taken

Taken by mouth as a single, one-time dose, as soon as possible after flu symptoms start or after exposure. The tablet dose is based on weight: 40 mg for patients weighing 40 kg to less than 80 kg, and 80 mg for patients weighing 80 kg or more. It may be taken with or without food, but it should not be taken with dairy products, calcium-fortified drinks, or antacids, laxatives, or oral supplements that contain calcium, iron, magnesium, selenium, or zinc.

Common side effects

In adults and adolescents the most common side effects were diarrhea (3%), bronchitis (3%), nausea (2%), sinusitis (2%), and headache (1%). In children 5 to under 12 years old, vomiting and diarrhea were each reported in 5%. Nasopharyngitis (a cold-like nose and throat inflammation) was the most frequent effect reported for flu prevention use.

Serious warnings

Serious allergic reactions have occurred, including anaphylaxis, angioedema (swelling), hives, and erythema multiforme; get emergency help for trouble breathing or swelling of the face, throat, or mouth. There is no evidence it works for illness caused by anything other than influenza viruses, and it does not prevent bacterial infections that can occur with the flu; if a bacterial infection is suspected it should be evaluated and treated. The label has no boxed warning.

Who should be careful

Do not use it if you have a history of allergy to baloxavir marboxil or any of its ingredients. It is not for children under 5 years of age. People with a milk or lactose sensitivity should note the tablets contain lactose monohydrate; tell your doctor about allergies and all medicines and supplements you take.

Major interactions

Products with polyvalent cations such as calcium, aluminum, or magnesium — including dairy products, calcium-fortified beverages, certain laxatives, antacids, and oral supplements with calcium, iron, magnesium, selenium, or zinc — can lower baloxavir levels and reduce how well it works, so avoid taking them together. Use with the intranasal live attenuated influenza vaccine (live flu nasal spray) has not been evaluated, and live vaccines may be affected.

Why it is in its tier

Baloxavir marboxil is most often placed on Tier 3. It is listed by 42.73% of Part D plans, and 69.21% of listing plans place it on Tier 3, which is a majority. Tier 3 is the preferred brand level, where you usually pay a mid-level flat copay or a share of the cost, called coinsurance, which is more than the low generic tiers but less than non-preferred tiers. Its single-dose brand form helps explain why it sits above the generic tiers in the data. For cost context, CMS reports average spending of $165.56 per beneficiary in 2024 as a CMS program average, not a copay, so it is not your exact cost for one dose. Individual plans vary, so check your own plan's tier and cost for this drug.

Sources

• XOFLUZA- baloxavir marboxil tablet, film coated — DailyMed
• MedlinePlus — National Library of Medicine
• MedlinePlus — Baloxavir Marboxil

What official patient guides say

Baloxavir marboxil comes as a tablet, a packet to be mixed with water, and a suspension (liquid) to take by mouth. Take it as a one-time dose, with or without food, exactly as directed. Do not take it along with dairy products such as milk or yogurt or with calcium-fortified drinks. If you are taking the suspension from a bottle, gently swirl the bottle before use to mix the medication evenly — do not shake the bottle — and use the oral syringe provided by your pharmacist to measure the correct amount; do not mix the suspension with any other liquid or with soft food, and do not take more or less of it than prescribed by your doctor. If you are using packets, empty the contents of a single packet into a container for each packet prescribed, add 15 to 20 mL of room temperature water, and drink it right away once the medicine has fully spread out in the water; repeat the process if an additional packet was prescribed. Because it is taken as a one-time dose, the page gives no missed-dose rule. Keep it in the container it came in, tightly closed and out of the reach of children, stored at room temperature away from excess heat and moisture, not in the bathroom. Take unneeded medicine to a take-back program instead of flushing it.

Source: MedlinePlus — Baloxavir Marboxil

Part D formulary coverage

Source: CMS Prescription Drug Plan Formulary, Pharmacy Network, and Pricing Information Files — Monthly file 2026-10-15 (plan year 2027), file 2027_20261008.zip (data.cms.gov dataset ed1496ea-23e7-41f1-9292-172fa842ccfb): basic drugs formulary file + plan information file, both dated 20261031 inside the zip; downloaded and aggregated 2026-10-30. Medication RxCUI sets resolved through the NLM RxNav (RxNorm) API.

What you pay

Without insurance, the cash benchmark is $161.9006 per unit (XOFLUZA 40 MG TABLET) — about $4857.02 for 30 units. NADAC benchmark — the average price pharmacies pay (CMS, as of 2026-11-04). Pharmacy shelf prices vary.

A tier is not a price; what you pay depends on your plan, pharmacy, and benefit stage; Extra Help or Medicaid can lower it further.

Sources: CMS Plan Benefit Package + formulary data; CMS NADAC · Checked 2026-11-07

Read next

• Part D in 2027: The $700 Deductible, the $2,400 Cap, and the $35 Insulin Rule
• Extra Help in 2027: Lower Drug Copays and Who Qualifies
• Checking Medicare Savings Programs and Extra Help

Part D spending averages (2024)

Source: CMS Medicare Part D Spending by Drug (Drug Spending Dashboard), release RY26 P04 V10, data through 2024 (DSD_PTD_RY26_P04_V10_DY24_BGM.csv), downloaded 2026-10-30

Companies covering this drug

2,348 plans from 264 companies list this drug on a formulary for 2027. Search by company or plan name, or filter by tier. Cost sharing is the plan's published amount for this drug's tier in the initial coverage stage (1-month retail supply), where the plan publishes it; a blank means the plan does not publish it.

A tier is not a price; what you pay depends on your plan, pharmacy, and benefit stage; Extra Help or Medicaid can lower it further.