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Baloxavir Marboxil

Medically reviewed by Last updated on Apr 4, 2020.


(ba LOX A veer mar BOX el)

Index Terms

  • S-033188
  • Xofluza

Dosage Forms

Excipient information presented when available (limited, particularly for generics); consult specific product labeling.

Tablet Therapy Pack, Oral:

Xofluza (40 MG Dose): 2 x 20 MG (2 ea)

Xofluza (80 MG Dose): 2 x 40 MG (2 ea)

Brand Names: U.S.

  • Xofluza (40 MG Dose)
  • Xofluza (80 MG Dose)

Pharmacologic Category

  • Antiviral Agent
  • Endonuclease Inhibitor


Baloxavir marboxil is an oral prodrug that is converted to baloxavir, an inhibitor of the endonuclease activity of a selective polymerase acidic (PA) protein, which is required for viral gene transcription, resulting in inhibition of influenza virus replication. Baloxavir has demonstrated antiviral activity against influenza A and B viruses, including strains resistant to standard current antiviral agents (Hayden 2018).


Vd: 1,180 L


Baloxavir marboxil is a prodrug; completely converted via UGT1A3 (major) and CYP3A4 (minor) to the active metabolite (baloxavir)


Feces (80.1%); Urine (14.7%; 3.3% as baloxavir)

Time to Peak

4 hours

Half-Life Elimination

79.1 hour

Protein Binding

~93% to 94%

Special Populations Note

Body weight: As weight increases, exposure to baloxavir decreases.

Use: Labeled Indications

Influenza, seasonal, treatment: Treatment of acute uncomplicated influenza (A or B) infection in patients ≥12 years of age who have been symptomatic for no more than 48 hours and who are otherwise healthy or at high risk of developing influenza-related complications.

Limitations of use: Influenza viruses change over time, and factors such as the virus type or subtype, emergence of resistance, or changes in viral virulence may diminish the clinical benefit of antiviral drugs. Consider available information on influenza drug susceptibility patterns and treatment effects when deciding whether to use baloxavir marboxil.


Hypersensitivity (eg, anaphylaxis, angioedema, urticaria, erythema multiforme) to baloxavir marboxil or any component of the formulation.

Dosing: Adult

Influenza, seasonal, treatment: Oral:

40 to <80 kg: 40 mg as a single dose within 48 hours of onset of influenza symptoms.

≥80 kg: 80 mg as a single dose within 48 hours of onset of influenza symptoms.

Dosing: Geriatric

Refer to adult dosing.

Dosing: Pediatric

Influenza, treatment: Note: Treatment should ideally begin within 48 hours of symptom onset.

Children <12 years: Limited data available (Baker 2020): Note: Available only as 20 mg tablets in the United States.

<20 kg: Oral: 2 mg/kg once as a single dose.

≥20 kg: Oral: 40 mg once as a single dose.

Children ≥12 years and Adolescents:

40 to <80 kg: Oral: 40 mg once as a single dose.

≥80 kg: Oral: 80 mg once as a single dose.

Influenza, prophylaxis (household contacts): Limited data available; optimal role in therapy not defined (Ikematsu 2020): Note: Available only as 20 mg tablets; study utilized a granule packet dosage form for patients <20 kg that is not available in the United States.

Children <12 years: Oral:

<10 kg: 1 mg/kg once as a single dose.

10 to <20 kg: 10 mg once as a single dose.

20 to <40 kg: 20 mg once as a single dose.

≥40 kg: 40 mg once as a single dose.

Children ≥12 years and Adolescents: Oral:

<80 kg: 40 mg once as a single dose.

≥80 kg: 80 mg once as a single dose.

Note: Dosing from a randomized, placebo-controlled study in which 374 patients received baloxavir marboxil (n=85 who were <20 years of age) after a household contact was diagnosed with influenza illness. Laboratory-identified clinical influenza occurred significantly less often in the baloxavir group overall than in the placebo group; however, efficacy was lower in patients <12 years of age (adjusted risk ratio 0.27 in <12 years compared to 0.10 in patients ≥12 years of age). Resistance-associated amino acid substitutions occurred in 15 patients after receipt of baloxavir, weigh risk to benefits (Ikematsu 2020).


Oral: Initiate within 48 hours of influenza symptom onset. Administer a single dose with or without food. Avoid administration with dairy products, calcium-fortified beverages, polyvalent cation-containing laxatives, antacids, or oral supplements (eg, calcium, iron, magnesium, selenium, zinc).


Store at 20°C to 25°C (68°F to 77°F); excursions permitted to 15°C to 30°C (59°F to 86°F). Store in original blister package.

Drug Interactions

Influenza Virus Vaccine (Live/Attenuated): Antiviral Agents (Influenza A and B) may diminish the therapeutic effect of Influenza Virus Vaccine (Live/Attenuated). Management: Avoid anti-influenza antivirals during the period beginning 48 hours prior to and ending 2 weeks after live influenza virus vaccine administration. Consider therapy modification

Polyvalent Cation Containing Products: May decrease the serum concentration of Baloxavir Marboxil. Avoid combination

Adverse Reactions

The following adverse drug reactions and incidences are derived from product labeling unless otherwise specified.

1% to 10%: Gastrointestinal: Diarrhea (2% [Hayden 2018])


Dermatologic: Erythema multiforme, facial swelling, skin rash, urticaria

Gastrointestinal: Bloody diarrhea, colitis, melena, swollen tongue, vomiting

Hypersensitivity: Anaphylactic shock, anaphylaxis, angioedema, hypersensitivity reaction, nonimmune anaphylaxis

Nervous system: Abnormal behavior, delirium, hallucination, voice disorder

Ophthalmic: Eyelid edema


Concerns related to adverse effects:

• Bacterial infection: There is no evidence of efficacy of baloxavir marboxil in illnesses (eg, bacterial infections) caused by pathogens other than influenza viruses. Serious bacterial infections may begin with influenza-like symptoms, may coexist with, or occur as an influenza complication. Baloxavir marboxil has not been shown to prevent such complications. Monitor for potential secondary bacterial infections and manage appropriately.

• Hypersensitivity: Hypersensitivity reactions, including anaphylaxis, angioedema, urticaria, and erythema multiforme have been reported; evaluate and treat accordingly.

Concurrent drug therapy issues:

• Drug-drug/drug-food interactions: Potentially significant interactions may exist, requiring dose or frequency adjustment, additional monitoring, and/or selection of alternative therapy. Consult drug interactions database for more detailed information.

Monitoring Parameters

Monitor for potential secondary bacterial infections.

Pregnancy Considerations

Adverse events were not observed in animal reproduction studies.

Untreated influenza infection is associated with an increased risk of adverse events to the fetus and an increased risk of complications or death to the mother. Other agents are currently recommended for the treatment of influenza in pregnant females and females up to 2 weeks postpartum (ACOG 2018; CDC [Fiore] 2011).

Patient Education

What is this drug used for?

• It is used to treat the flu.

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

• Diarrhea

• Common cold symptoms

• Nose irritation

• Throat irritation

• Headache

• Nausea

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

• Dizziness

• Passing out

• Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.

Note: This is not a comprehensive list of all side effects. Talk to your doctor if you have questions.

Consumer Information Use and Disclaimer: This information should not be used to decide whether or not to take this medicine or any other medicine. Only the healthcare provider has the knowledge and training to decide which medicines are right for a specific patient. This information does not endorse any medicine as safe, effective, or approved for treating any patient or health condition. This is only a limited summary of general information about the medicine’s uses from the patient education leaflet and is not intended to be comprehensive. This limited summary does NOT include all information available about the possible uses, directions, warnings, precautions, interactions, adverse effects, or risks that may apply to this medicine. This information is not intended to provide medical advice, diagnosis or treatment and does not replace information you receive from the healthcare provider. For a more detailed summary of information about the risks and benefits of using this medicine, please speak with your healthcare provider and review the entire patient education leaflet.

Frequently asked questions

Further information

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