FDA Approval Date for Baloxavir Marboxil (Xofluza)
Baloxavir marboxil (Xofluza) was initially approved by the FDA in October 2018 1.
Initial Approval Details
The FDA licensed baloxavir marboxil in 2018 for the early treatment of uncomplicated influenza in outpatients 12 years and older who have been ill for no more than 2 days 2. This represented the first cap-dependent endonuclease inhibitor approved for influenza treatment, introducing a novel mechanism of action distinct from neuraminidase inhibitors 3, 4.
Subsequent FDA Approvals
Following the initial 2018 approval, the FDA has expanded the indications and approved additional formulations:
November 2020: FDA approved baloxavir for post-exposure prophylaxis of influenza in patients 12 years and older 5
Recent expansions: The current FDA labeling now includes treatment and post-exposure prophylaxis for patients 5 years and older (expanded from the original 12 years and older indication) 1
May 2025: Most recent major labeling changes to dosage and administration 1
Clinical Context
The approval came after clinical trials demonstrated that baloxavir was noninferior to oseltamivir for symptom relief while offering the advantage of single-dose administration 3, 6. The drug works by inhibiting the influenza virus polymerase acidic (PA) endonuclease, preventing viral RNA replication through a mechanism completely different from existing neuraminidase inhibitors 4.
Important caveat: Despite being approved in 2018, treatment-emergent resistance was detected even during initial clinical trials, with the I38 mutation in the cap-dependent endonuclease conferring reduced susceptibility to baloxavir 7, 6. This resistance pattern has been particularly notable in younger pediatric patients, which is why the drug is not indicated for children under 5 years of age 1.