PHILADELPHIA, PA — GSK plc (NYSE: GSK) secured U.S. Food and Drug Administration approval for Hibsago, a hepatitis B treatment that achieved functional cure in 19% of eligible clinical trial participants, offering some patients a potential alternative to indefinite antiviral therapy.
The approval covers Hibsago, also known as bepirovirsen, in combination with existing nucleos(t)ide analogue reverse transcriptase inhibitor therapy for adults with chronic hepatitis B who do not have cirrhosis.
Eligible patients must have received antiviral treatment for at least six months, have suppressed hepatitis B viral DNA and have hepatitis B surface antigen levels of 3,000 international units per milliliter or less, as measured by an FDA-authorized test.
The decision establishes a new treatment option for a chronic infection affecting approximately 1.7 million people in the United States. Existing antiviral medications can suppress hepatitis B but rarely produce the sustained response needed to discontinue treatment.
Hibsago is administered over six months, with patients able to self-administer the medication after the initial dose.
The FDA granted approval following Priority Review and Breakthrough Therapy designation, reflecting the treatment’s potential improvement over existing therapies.
The decision was supported by two Phase III clinical trials, B-Well 1 and B-Well 2, which met their primary endpoints.
Pooled results showed that 233 of 1,220 patients receiving bepirovirsen, or 19%, achieved functional cure, compared with none of the 614 patients in the placebo group. Participants continued background antiviral treatment as part of the studies.
Functional cure was defined as undetectable hepatitis B viral DNA and surface antigen for at least 24 weeks after discontinuing all treatment.
Unlike complete eradication of the virus, functional cure indicates sustained immune control without medication.
The results compare with functional cure rates typically below 1% after one year of existing standard treatment, according to GSK.
The strongest responses occurred among patients entering treatment with lower concentrations of hepatitis B surface antigen.
In participants with baseline antigen levels of 1,000 IU/mL or less, 26% of those receiving bepirovirsen achieved functional cure, representing 200 of 768 patients. None of the 393 placebo recipients in that subgroup achieved the same outcome.
GSK said patients with antigen levels at or below that threshold account for approximately 45% of diagnosed chronic hepatitis B cases globally.
Additional exploratory findings showed that 49% of bepirovirsen recipients in the overall study population had surface antigen levels reduced to 100 IU/mL or less by week 72. The proportion reached 62% among participants whose baseline levels were 1,000 IU/mL or lower.
Those measurements are distinct from functional cure but may indicate improved immune control of the infection.
The most frequently observed adverse events were redness and pain at the injection site and temporary elevations in a liver enzyme.
Hibsago belongs to a class of medicines known as antisense oligonucleotides. It is designed to interfere with viral RNA production, reducing hepatitis B proteins and potentially allowing the immune system to maintain control of the infection.
GSK licensed bepirovirsen from Ionis and collaborated with the company on its development.
“Despite current therapies, many people living with chronic hepatitis B remain on treatment indefinitely and continue to face the risk of serious liver complications,” said Tony Wood, GSK’s chief scientific officer.
Chronic hepatitis B can cause progressive liver damage and increase the risk of cirrhosis and liver cancer, making sustained control of the infection a major treatment objective.
The approval also introduces a diagnostic requirement into treatment selection. Physicians must use an FDA-authorized quantitative hepatitis B surface antigen test to determine whether patients meet the prescribing criteria.
Hibsago is already approved in Japan, and GSK is pursuing additional regulatory approvals in other markets, including China, where the treatment has received Breakthrough Therapy and Priority Review designations.
The U.S. authorization gives GSK another approved medicine in its infectious disease portfolio while establishing a six-month treatment approach for a defined group of chronic hepatitis B patients.
The clinical results also indicate that functional cure remains limited to a minority of treated patients, underscoring the distinction between improving the likelihood of sustained viral control and reliably eliminating the need for ongoing treatment.
Support the local news that supports Chester County. MyChesCo delivers reliable, fact-based reporting and essential community resources—free for everyone. If you value that, click here to become a patron today.