FDA approves GSK's Hibsago as first antisense drug for chronic hepatitis B

The US Food and Drug Administration approved GSK's Hibsago (bepirovirsen) on 20 October 2026 for chronic hepatitis B in certain adults without cirrhosis, to be given alongside their existing antiviral therapy¹. It is the first antisense oligonucleotide the FDA has approved for the disease¹.

What the approval covers

The label is narrow. Patients must have been on hepatitis B antiviral therapy for at least six months, have suppressed virus in their blood and have a hepatitis B surface antigen (HBsAg) level of 3,000 IU/mL or less, measured with an FDA-authorised test¹. The FDA authorised Roche's Elecsys HBsAg II quant II RxDx assay at the same time as the companion diagnostic, both to select patients and to monitor them through treatment¹.

Hibsago is injected under the skin for up to 24 weeks. Patients keep taking their usual hepatitis B medicine during that time and for at least 24 weeks after the last injection, and some may then stop it if they meet set clinical and laboratory criteria¹. The drug targets the genetic instructions the virus uses to copy itself and make viral proteins, lowering both viral load and surface antigen¹.

The evidence comes from two placebo-controlled trials¹. In the FDA's summary, 24% of Hibsago patients qualified to stop their existing medicine against none on placebo, and 19% still had the virus under control with no detectable HBsAg 24 weeks after stopping all treatment¹. GSK's pooled analysis of the Phase III B-Well 1 and B-Well 2 trials, run in 29 countries and published in the New England Journal of Medicine in May, gave the same 19% functional cure rate (233 of 1,220 against 0 of 614 on placebo)². In patients starting at 1,000 IU/mL HBsAg or below, the rate was 26% (200 of 768 against 0 of 393)². GSK puts the functional cure rate on current standard care at under 1%².

The FDA gave the drug Fast Track and Breakthrough Therapy designations and Priority Review¹. Wendy Carter, Acting Director of the FDA's Office of Infectious Diseases, said the drug "gives some patients the possibility of maintaining control of the virus after all chronic HBV treatment has ended"¹.

What it means for the market

The approval moves the commercial goal in hepatitis B from lifelong viral suppression towards a finite course of treatment for a defined subgroup. GSK says the disease affects more than 240 million people worldwide, including 1.7 million in the US and 75 million in China, and accounts for about 56% of liver cancer cases². GSK also says the 1,000 IU/mL subgroup makes up roughly 45% of diagnosed cases globally².

The tie to a quantitative antigen test matters for providers and payers: access depends on a lab result, so diagnostic capacity becomes part of the launch. Roche gains a companion diagnostic role in the same decision¹. GSK licensed bepirovirsen from Ionis and developed it with that company². In May GSK agreed a collaboration with Sino Biopharmaceutical aimed at access at launch in China, and the drug was also under review in Europe and China².

Caveats

The benefit applies to a minority: around four in five treated patients in the trials did not reach functional cure¹². Hibsago carries a boxed warning for serious liver reactions and for low platelet counts that can raise the risk of life-threatening bleeding, with further warnings on kidney function, vasculitis and other inflammatory reactions¹. Patients need regular blood tests before and during treatment¹. The most common side effects were injection site reactions, fever, fatigue and headache¹. The approval does not cover people with cirrhosis, or those whose surface antigen is above 3,000 IU/mL¹.