FDA Approves Hibsago, First Antisense Hepatitis B Therapy That May Let Some Patients Stop Lifelong Medication

The US Food and Drug Administration has approved a new drug for chronic hepatitis B called Hibsago, and the approval carries a possibility that standard treatments have rarely offered: for some patients, staying in control of the virus after all therapy has stopped.

Hibsago, known chemically as bepirovirsen, is the first antisense oligonucleotide the agency has cleared for chronic hepatitis B. It is not a stand-alone treatment. It is approved for use alongside existing antiviral therapy in certain adults who do not have cirrhosis. To qualify, a patient must have been on hepatitis B antivirals for at least six months, have suppressed virus in the blood, and have hepatitis B surface antigen levels of 3,000 international units per millilitre or lower, as measured by an FDA-authorised test.

The agency also authorised a companion diagnostic, the Roche Elecsys HBsAg II quant II RxDx assay, to help choose patients for treatment and to monitor them while they are on it.

The drug works by targeting the genetic instructions the virus uses to copy itself and to make viral proteins. That helps reduce both the amount of virus and the level of surface antigen in the body. Chronic hepatitis B is a long-term liver infection that can progress to cirrhosis and raises the risk of liver cancer. The virus spreads through infected bodily fluids such as blood, saliva and semen.

The approval rests on two clinical trials that compared Hibsago with a placebo. Patients received injections under the skin for up to 24 weeks while continuing their existing hepatitis B medicine, and kept taking that medicine for at least 24 weeks after their last injection. Those who then met certain health and laboratory requirements could stop it. Across the two trials, 24 per cent of patients given Hibsago met those requirements, compared with none on placebo. Twenty-four weeks after stopping all hepatitis B treatment, 19 per cent of Hibsago patients still had the virus under control, with surface antigen undetectable in their blood. That is nearly one in five.

Dr Wendy Carter, Acting Director of the Office of Infectious Diseases in the FDA's Center for Drug Evaluation and Research, noted that many people with chronic hepatitis B take antiviral medication for years to keep the virus suppressed. She said Hibsago gives some patients the possibility of keeping control of the virus after chronic treatment ends, and called the approval an important advance.

The drug carries real risks. It has a boxed warning for serious liver reactions and for low platelet counts, which can raise the risk of life-threatening bleeding. Further warnings cover worsening kidney function, serious inflammatory reactions such as vasculitis, and serious risks if the injection is not given properly. Patients need regular blood tests and follow-up before and during treatment. The most common side effects, setting aside laboratory abnormalities, are injection site reactions, fever, fatigue and headache.

The scale of the problem explains the interest. More than 250 million people worldwide live with chronic hepatitis B. Current standard treatments help only one to four per cent of patients clear the virus for a sustained period, what doctors call a functional cure. Nucleotide analogues, a widely used class of treatment, are often taken for life and suppress the virus but rarely eliminate it.

The FDA granted Hibsago Fast Track and Breakthrough Therapy designations, along with Priority Review. The approval went to GSK plc, which licensed the drug from Ionis Pharmaceuticals. Hibsago is already approved in Japan and is under review in China and Europe. For GSK, under new chief executive Luke Miels, the drug matters commercially: the company expects peak annual sales above £2 billion, and it is central to a goal of more than £40 billion in annual revenue by 2031, as patents on its blockbuster HIV drugs approach expiry. A rival therapy, pevifoscorvir sodium from US biotech Aligos Therapeutics, is being tested in a mid-stage trial.