FDA Approves Hibsago as First Antisense Oligonucleotide Treatment for Chronic Hepatitis B

The U.S. Food and Drug Administration announced on Tuesday that it has approved Hibsago (bepirovirsen) injection for the treatment of chronic hepatitis B virus (HBV) infection in certain adults without cirrhosis. The drug, which is designed to be used in combination with existing antiviral therapy, is the first antisense oligonucleotide approved by the agency for this condition.

The approval applies to adult patients without cirrhosis who have undergone HBV antiviral therapy for at least six months, have suppressed levels of HBV in their blood, and maintain hepatitis B surface antigen (HBsAg) levels of 3,000 IU/mL or less, verified through an FDA-authorized test. Along with the drug approval, the FDA authorized the Roche Elecsys HBsAg II quant II RxDx assay as a companion diagnostic to help select and monitor eligible patients.

According to the FDA, Hibsago functions by targeting the genetic instructions that HBV uses to replicate and produce viral proteins, reducing viral load and surface antigen levels in the body. In clinical trials, the medication was administered via subcutaneous injection for up to 24 weeks alongside standard antiviral drugs. Patients continued their baseline antiviral therapy for at least 24 weeks following their final Hibsago dose, after which some individuals could discontinue all treatment if specific health and laboratory criteria were met.

Across two clinical trials comparing the drug against a placebo, 24% of patients receiving Hibsago met the criteria to discontinue baseline antiviral medication, compared to 0% in the placebo group. The agency reported that 24 weeks after halting all hepatitis B therapies, 19% of Hibsago-treated patients maintained viral control and had undetectable levels of HBsAg in their blood.

The medication's labeling includes a boxed warning for serious liver reactions and low platelet counts, which can elevate the risk of life-threatening bleeding. Additional warnings address risks of declining kidney function, severe inflammatory reactions such as vasculitis, and hazards associated with improper injection administration. The FDA noted that the most common non-laboratory side effects include injection site reactions, fever, fatigue, and headache.

Hibsago received Fast Track, Breakthrough Therapy, and Priority Review designations prior to approval. The regulatory approval was granted to pharmaceutical company GSK plc.

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