The U.S. Food and Drug Administration approved bepirovirsen (Hibsago; GSK) as an injection for use with existing antiviral therapy to treat chronic hepatitis B virus infection in patients without cirrhosis. The designation marks the first antisense oligonucleotide approved for this specific indication, announced by the agency on October 20, 2026.
Hibsago provides a new treatment approach that gives some patients the possibility of maintaining control of the virus after all chronic HBV treatment has ended, stated Wendy Carter, acting director of the Office of Infectious Diseases in the Center for Drug Evaluation and Research at the FDA. This approval represents an important advance for people living with this serious disease, she added. The medication is marketed under the brand name Hibsago by GlaxoSmithKline (GSK).
Bepirovirsen targets the genetic instructions HBV uses to replicate and produce viral proteins. The FDA specified the medication is for patients who have received HBV antiviral therapy for at least six months, have suppressed HBV levels in their blood, and show hepatitis B surface antigen, or HBsAg, levels of 3,000 IU/mL or less. A companion diagnostic device from Roche, the Elecsys HBsAg II quant II RxDx assay, was also authorized to identify eligible patients and monitor treatment progress throughout the course of therapy. This assay enables precise measurement of HBsAg levels, critical for determining patient eligibility and tracking therapeutic response.
Trial Results Supporting Approval
Phase 3 trials B-Well 1 (NCT05630807) and B-Well 2 (NCT05630820) provided the evidence base for the approval. Pooled analysis of 1,220 participants showed that six months of bepirovirsen treatment achieved a functional cure rate of 19 percent, compared to zero percent in the 614-placebo group. Both trials met their primary endpoints with statistically significant improvements in functional cure rates.
A subgroup analysis focused on participants with HBsAg levels of 1,000 IU/mL or less, representing roughly 45 percent of global chronic HBV cases, revealed a 26 percent functional cure rate (200 of 768 participants). At week 72, exploratory data indicated that 49 percent of all treated participants and 62 percent of those in the lower HBsAg subgroup achieved HBsAg levels at or below 100 IU/mL.
Safety Considerations and Expert Perspective
The trials identified an acceptable safety profile, with common adverse events including injection site erythema, local pain, and transient elevations in a liver enzyme. However, bepirovirsen carries a boxed warning for serious liver reactions and low platelet counts, which may increase bleeding risk. Additional warnings address potential kidney function worsening, inflammatory reactions, and risks from improper administration. Regular blood monitoring and healthcare provider follow-up are required during treatment to mitigate these risks. The Elecsys HBsAg assay plays a critical role in this monitoring process, enabling clinicians to track HBsAg trends and adjust care plans accordingly.