Is baloxavir marboxil (Xofluza) effective for treatment of influenza B infection?

Does Xofluza Work for Flu B?

Yes, baloxavir marboxil (Xofluza) is effective against influenza B and demonstrates activity against both influenza A and B viruses, though oseltamivir remains the preferred first-line agent for most patients. 1, 2

Antiviral Spectrum and Mechanism

• Baloxavir is a selective inhibitor of influenza cap-dependent endonuclease with demonstrated activity against both influenza A and B viruses in preclinical models and clinical trials. 3, 4
• The drug works through a novel mechanism distinct from neuraminidase inhibitors, targeting the viral polymerase acidic protein to prevent viral mRNA transcription. 4, 5

Clinical Efficacy Against Influenza B

• Baloxavir demonstrates superior efficacy compared to oseltamivir specifically for influenza B infections in adolescents and adults, according to the American Academy of Pediatrics. 2
• In postmarketing surveillance of over 3,000 Japanese patients, baloxavir showed consistent effectiveness regardless of influenza virus type, with median time to symptom alleviation of 2.5 days for both influenza A and B. 6
• The median time to fever resolution was 1.5 days for both influenza A and B groups treated with baloxavir. 6

Comparative Effectiveness

• Baloxavir provides similar overall clinical outcomes to neuraminidase inhibitors in terms of symptom duration but reduces viral shedding more rapidly than oseltamivir. 2, 7
• In phase 3 trials, baloxavir was superior to placebo in alleviating influenza symptoms and superior to both oseltamivir and placebo in reducing viral load 1 day after treatment initiation. 7

Current Guideline Recommendations

Despite baloxavir's efficacy against influenza B, oseltamivir remains the preferred first-line agent for most clinical scenarios. 1, 8

• The American Academy of Pediatrics considers oral oseltamivir the antiviral drug of choice for management of influenza virus infections, including influenza B, based on cumulative experience in children, relative cost, and ease of administration. 1
• Baloxavir is approved for treatment of acute uncomplicated influenza in otherwise healthy patients ≥12 years of age and those at high risk of developing complications. 1, 2

Critical Resistance Concerns

• Treatment-emergent resistance is a significant concern with baloxavir, particularly in young children and those infected with influenza A(H3N2), with resistance mutations (PA/I38T/M/F substitutions) emerging in 2.2% to 9.7% of treated patients. 2, 7, 5
• The Centers for Disease Control and Prevention notes that globally, reduced susceptibility to baloxavir was observed in 0.5% during the 2018-2019 season and 0.1% during the 2019-2020 season. 2

Specific Patient Populations

• The American Academy of Pediatrics recommends oseltamivir as the drug of choice for patients with a history of respiratory or cardiac disease due to more extensive cumulative experience, lower cost, and established efficacy data in high-risk patients. 2
• Baloxavir is not routinely recommended for immunocompromised patients due to limited efficacy data and emergence of resistant strains, according to the National Comprehensive Cancer Network. 2
• For hospitalized children, oseltamivir is the only drug recommended by the American Academy of Pediatrics. 1

Dosing and Administration

• Baloxavir is administered as a single weight-based dose: 40 mg for patients <80 kg and 80 mg for patients ≥80 kg, given within 48 hours of symptom onset. 3, 7
• This single-dose regimen represents a significant practical advantage over oseltamivir's 5-day twice-daily dosing. 3, 4

Safety Profile

• Baloxavir is well tolerated with only mild adverse events reported, including nausea, headache, diarrhea, bronchitis, and nasopharyngitis. 3
• In postmarketing surveillance, adverse drug reactions occurred in 11.2% of patients, with diarrhea (6.1%) being most common; 98.9% of reactions were non-serious. 6
• There are no absolute contraindications to baloxavir use, though hypersensitivity reactions including anaphylaxis have been reported postmarketing. 2

Clinical Decision Algorithm

For influenza B specifically:

• Otherwise healthy patients ≥12 years with uncomplicated influenza B: Baloxavir is an acceptable alternative to oseltamivir, offering single-dose convenience and potentially superior efficacy. 2, 7
• Patients with chronic respiratory or cardiac disease: Choose oseltamivir over baloxavir due to more extensive safety data. 2
• Immunocompromised patients: Avoid baloxavir; use oseltamivir instead. 2
• Hospitalized patients or children <12 years: Use oseltamivir as first-line therapy. 1