FDA Approves Hibsago, First Antisense Drug for Chronic Hepatitis B, Offering a Path to Functional Cure

On October 20, 2026, the US Food and Drug Administration approved Hibsago, the brand name for bepirovirsen, as a treatment for certain adults with chronic hepatitis B. It is the first antisense oligonucleotide the agency has cleared for the disease, and in clinical trials it helped some patients keep the virus under control after they stopped every hepatitis B medicine.

The approval went to GSK plc, which licensed bepirovirsen from Ionis and developed it together with that company. The US decision follows Japan, which approved the drug in August 2026, the first approval anywhere in the world.

The standard of care today is a daily antiviral tablet, the class known as nucleos(t)ide analogues. These suppress the virus but rarely clear it, so many patients take them for years. The source puts the chance of a functional cure on these drugs at about 1%. Wendy Carter, DO, acting director of the Office of Infectious Diseases in the FDA's Center for Drug Evaluation and Research, said Hibsago offers a new approach that gives some patients the possibility of maintaining control of the virus after all chronic HBV treatment has ended, calling the approval an important advance.

The drug works on the genetic material the virus uses to make its proteins. By lowering viral RNA and hepatitis B surface antigen (HBsAg), a viral protein and key marker of infection, it helps the immune system take control, including after treatment ends. It is injected under the skin for up to 24 weeks, alongside the patient's existing hepatitis B medicine. In the trials the dose was 300 mg once a week. Patients then continue their regular treatment for at least 24 weeks after the last injection, and may stop all treatment if they meet set clinical and laboratory criteria. The FDA also authorized a diagnostic test to identify eligible patients and monitor them.

The approval rests on two Phase 3 trials, B-Well 1 and B-Well 2, which compared Hibsago with placebo in adults already on antiviral treatment. They ran across 29 countries and enrolled more than 1,800 patients. Across both, 24% of those on Hibsago met the criteria to stop their antiviral medicine, against none in the placebo groups. Twenty-four weeks after stopping all treatment, 19% of Hibsago patients still had the virus under control, with no detectable HBsAg in their blood.

Results were better for people who started with lower HBsAg levels. Among those below 1,000 IU/mL, the functional cure rate reached 25% in B-Well 1 and 28% in B-Well 2. That matters because functional cure is linked to a much lower risk of long-term liver problems, including liver cancer, and of death from any cause.

The drug carries real warnings. These include serious liver reactions, thrombocytopenia (low platelet count, which can raise the risk of life-threatening bleeding), poor kidney function, and inflammatory reactions such as vasculitis. In the trials, serious side effects of grade 3 or higher occurred in 16% of Hibsago patients versus 3% on placebo, with raised liver enzymes the most common. Patients need regular blood tests and close medical checks before and during treatment.

Hibsago received Fast Track and Breakthrough Therapy designations and Priority Review. It is approved for adults without cirrhosis who have taken antiviral medicine for at least six months, have suppressed HBV levels, and meet specific HBsAg criteria. Experts stress it is not for everyone with chronic hepatitis B, and eligibility will turn on liver health, current treatment, viral suppression and lab results. Patients are advised to discuss it with their doctors.