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Baloxavir marboxil (Oral)

Generic name: baloxavir marboxil [ bal-OX-a-vir-mar-BOX-il ]
Drug class: Miscellaneous antivirals

Medically reviewed by Last updated on Nov 10, 2022.

Uses for baloxavir marboxil

Baloxavir marboxil is used to treat the flu (influenza) in patients who have had flu symptoms (eg, cough, fever, runny nose, headache, joint or muscle pain) for not more than 48 hours. It is used in patients 5 years of age and older who are healthy or in patients 12 years of age and older who are at high risk of developing flu-related complications.

Baloxavir marboxil is also used to prevent flu in patients 5 years of age and older who have been exposed with the virus (post-exposure prophylaxis).

This medicine is available only with your doctor's prescription.

Before using baloxavir marboxil

In deciding to use a medicine, the risks of taking the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For this medicine, the following should be considered:


Tell your doctor if you have ever had any unusual or allergic reaction to this medicine or any other medicines. Also tell your health care professional if you have any other types of allergies, such as to foods, dyes, preservatives, or animals. For non-prescription products, read the label or package ingredients carefully.


Appropriate studies have not been performed on the relationship of age to the effects of baloxavir marboxil in children younger than 5 years of age. Safety and efficacy have not been established.


Appropriate studies performed to date have not demonstrated geriatric-specific problems that would limit the usefulness of baloxavir marboxil in the elderly.

Breast Feeding

There are no adequate studies in women for determining infant risk when using this medication during breastfeeding. Weigh the potential benefits against the potential risks before taking this medication while breastfeeding.

Interactions with Medicines

Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are taking this medicine, it is especially important that your healthcare professional know if you are taking any of the medicines listed below. The following interactions have been selected on the basis of their potential significance and are not necessarily all-inclusive.

Using this medicine with any of the following medicines is usually not recommended, but may be required in some cases. If both medicines are prescribed together, your doctor may change the dose or how often you use one or both of the medicines.

  • Aluminum
  • Calcium
  • Iron
  • Magnesium
  • Selenium
  • Zinc

Interactions with Food/Tobacco/Alcohol

Certain medicines should not be used at or around the time of eating food or eating certain types of food since interactions may occur. Using alcohol or tobacco with certain medicines may also cause interactions to occur. Discuss with your healthcare professional the use of your medicine with food, alcohol, or tobacco.

Other Medical Problems

The presence of other medical problems may affect the use of this medicine. Make sure you tell your doctor if you have any other medical problems, especially:

  • Infection (bacterial)—May have the same symptoms as flu. This medicine will not treat or prevent this condition.

Proper use of baloxavir marboxil

Take this medicine only as directed by your doctor. Do not take more of it, do not take it more often, and do not take it for a longer time than your doctor ordered.

This medicine should come with a patient information leaflet. Read and follow these instructions carefully. Ask your doctor or pharmacist if you have any questions.

Take this medicine with or without food. However, do not take this medicine with dairy products or drinks rich in calcium. Also, do not use this medicine together with antacids, laxatives, or oral supplements containing calcium, iron, magnesium, selenium, or zinc.

Do not use this medicine if you have received the nasal flu vaccine (live attenuated influenza vaccine), unless your doctor says it is okay.

This medicine works best if taken within 48 hours of having flu symptoms (eg, weakness, headache, fever, cough, runny or stuffy nose, sore throat). Keep using this medicine for the full time of treatment even if you begin to feel better after a few days. This will help clear up your infection completely. If you stop using this medicine too soon, your symptoms may return.

If your child is unable to swallow the tablets whole, you may use the oral liquid.

To use the oral liquid:

  • Your pharmacist will prepare the oral liquid. Talk to your pharmacist if it is not given to you as a liquid or if you did not receive a measuring device.
  • Swirl the bottle before each use. Do not shake.
  • Measure the medicine with the provided oral dosing syringe or measuring cup.
  • You should sit upright when taking this medicine. Do not mix it with soft food or another liquid.
  • If it is given through a feeding tube: Using a syringe, rinse the feeding tube with 1 milliliter (mL) of water. Then, inject the oral syringe with medicine into the feeding tube and rinse the tube with 1 mL water.


The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

  • For the flu:
    • For oral dosage form (suspension):
      • Adults and children 5 years of age and older weighing 80 kilograms (kg) or more—80 mg or 40 milliliters (mL) (2 bottles) taken as a single dose.
      • Adults and children 5 years of age and older weighing 20 kg to less than 80 kg—40 mg or 20 mL (1 bottle) taken as a single dose.
      • Children 5 years of age and older weighing less than 20 kg—Dose is based on body weight and must be determined by your doctor. The dose is usually 2 mg per kilogram (kg) of body weight (less than 1 bottle) taken as a single dose.
      • Children younger than 5 years of age—Use and dose must be determined by your doctor.
    • For oral dosage form (tablets):
      • Adults and children 5 years of age and older weighing 80 kilograms (kg) or more—80 milligrams (mg) taken as a single dose per day.
      • Adults and children 5 years of age and older weighing 20 kg to less than 80 kg—40 mg taken as a single dose per day.
      • Children younger than 5 years of age—Use and dose must be determined by your doctor.

Missed Dose

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.


Store the medicine in a closed container at room temperature, away from heat, moisture, and direct light. Keep from freezing.

Keep out of the reach of children.

Do not keep outdated medicine or medicine no longer needed.

Ask your healthcare professional how you should dispose of any medicine you do not use.

Throw away any unused liquid within 10 hours of mixing.

Precautions while using baloxavir marboxil

It is very important that your doctor check your or your child's progress after treatment to make sure that the infection is cleared up completely, and to allow your doctor to check for any unwanted effects.

If your or your child's symptoms do not improve or if they become worse, check with your doctor.

This medicine may cause serious allergic reactions, including anaphylaxis, angioedema, or certain skin conditions, which can be life-threatening and require immediate medical attention. Call your doctor right away if you or your child have a rash, itching, blistering, peeling, or loosening of the skin, fever or chills, large, hive-like swelling on face, eyelids, lips, tongue, throat, hands, legs, feet, or sex organs, trouble breathing or swallowing, or any swelling of your hands, face, mouth, or throat while you are using this medicine.

This medicine is not a substitute for an annual flu shot. It also will not keep you or your child from getting a bacterial infection that starts with flu-like symptoms.

Side Effects of baloxavir marboxil

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur:

Less common

  • Chest tightness
  • cough producing mucus
  • difficulty breathing
  • fever
  • headache
  • muscle aches
  • sore throat
  • stuffy or runny nose
  • unusual tiredness or weakness

Incidence not known

  • Blistering, peeling, or loosening of the skin
  • bloody, black, or tarry stools
  • chills
  • cough
  • diarrhea
  • difficulty swallowing
  • dizziness
  • fast heartbeat
  • hives, itching, skin rash
  • hoarseness
  • joint or muscle pain
  • puffiness or swelling of the eyelids or around the eyes, face, lips, or tongue
  • red, irritated eyes
  • sores, ulcers, or white spots in the mouth or on the lips
  • voice changes

Some side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects. Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

Less common

  • Nausea

Incidence not known

  • Seeing, hearing, or feeling things that are not there
  • vomiting

Other side effects not listed may also occur in some patients. If you notice any other effects, check with your healthcare professional.

Call your doctor for medical advice about side effects. You may report side effects to the FDA at 1-800-FDA-1088.

Frequently asked questions

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.