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FDA Approves Hibsago, GSK's Hepatitis B Drug From Ionis, With 10-12% Royalties And A Boxed Warning

The six-month treatment showed a 19% functional cure rate in pooled late-stage trials, and its label warns of liver flares and low platelets.

Matteo Parrino Jonathan Ponciano

Matteo Parrino, Jonathan Ponciano

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FDA Approves Hibsago, GSK's Hepatitis B Drug From Ionis, With 10-12% Royalties And A Boxed Warning

The FDA approved Hibsago (bepirovirsen), a chronic hepatitis B drug GSK licensed from Ionis, Ionis said in an 8-K filed Wednesday covering a Tuesday announcement. Ionis is eligible for tiered royalties of 10-12% on net sales under its 2019 license with GSK.

What the approval covers

The approval is for adults without cirrhosis who have taken nucleos(t)ide analogue antiviral therapy for at least 6 months, have suppressed viral DNA, and have surface antigen levels at or below 3000 IU/ml, as measured by an FDA-authorized test. Hibsago is used in combination with that therapy, according to the press release furnished with the filing.

The FDA granted it under priority review and Breakthrough Therapy Designation. The release describes a six-month treatment with an option of at-home administration after the first dose.

Pooled Phase 3 B-Well data showed a 19% functional cure rate, or 233 of 1,220 patients, versus 0 of 614 on placebo. Standard care alone typically achieves under 1% after one year, the release says. Functional cure means the virus and surface antigen stay undetectable for at least 24 weeks after all treatment stops.

In patients with surface antigen at or below 1000 IU/ml, a key secondary measure, the rate was 26% (200 of 768 versus 0 of 393 on placebo). The release says that group is about 45% of diagnosed cases globally.

The boxed warning and what it means for Ionis

The label carries a boxed warning, the FDA's most prominent safety alert, for on-treatment hepatic flares and for thrombocytopenia (low platelet counts), which can be life-threatening. Platelet counts must be checked before treatment and at least weekly during it. The release lists injection site reactions, fever, fatigue and headache as the most common adverse reactions.

For Ionis, the economics are royalties and milestones. It has already received an upfront payment, a license fee and development and regulatory milestones, and remains eligible for further regulatory and sales milestones. BioSpace reported that Hibsago is Ionis's third antisense approval this year, after Zanvastro in September and Tryngolza in June, and cited a BMO note calling the royalty contribution a relatively modest part of Ionis's commercial business.

Ionis shares closed at $44.27 at Wednesday's close, down about 2%, before the filing was accepted at 4:15 p.m. ET.

What to watch

GSK said Hibsago should reach U.S. patients before year-end, with list price to follow payer talks, per Fierce Pharma. The release also says GSK is pursuing approvals in other regions, with key decisions anticipated in the coming months.

Ionis CEO Brett P. Monia said the company believes Hibsago offers "the potential to achieve unprecedented functional cure rates after a six-month treatment course."

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