The U.S. Food and Drug Administration has approved Hibsago (bepirovirsen), developed by GSK in collaboration with Ionis Pharmaceuticals (NASDAQ: IONS), for the treatment of chronic hepatitis B virus infection in adult patients without cirrhosis who have been on nucleos(t)ide analogue therapy for at least six months with suppressed HBV DNA and HBV surface antigen levels at or below 3,000 IU/ml.

The approval was granted under FDA priority review and Breakthrough Therapy Designation. Bepirovirsen is also approved in Japan and has received Breakthrough Therapy and Priority Review designation in China, as well as SENKU designation in Japan.

Phase 3 B-Well trial data, conducted across 29 countries, showed a functional cure rate of 19% in adults with HBsAg levels at or below 3,000 IU/ml, compared to less than 1% with current standard of care alone after one year of treatment. In participants with HBsAg at or below 1,000 IU/ml, the functional cure rate reached 26%. Functional cure is defined as undetectable HBV DNA and HBsAg for at least 24 weeks after stopping all treatment.

The treatment course is six months, with the option for at-home administration after the first dose. Chronic hepatitis B affects approximately 1.7 million people in the U.S. and more than 240 million worldwide.

The drug carries a boxed warning for on-treatment hepatic flares and thrombocytopenia. The most common adverse reactions included injection site reactions, fever, fatigue, and headache.

GSK licensed bepirovirsen from Ionis in 2019. Under the agreement, Ionis is eligible to receive tiered royalties of 10% to 12% on net sales, along with additional regulatory and sales milestone payments. GSK is continuing regulatory submissions for bepirovirsen in other geographies.