Mirum Posts 59% Phase 3 Hepatitis D Response, Setting Up A First-Half 2027 FDA Filing

Mirum Pharmaceuticals reported another phase 3 win for brelovitug in chronic hepatitis D, extending a run that now includes two successful late-stage studies and setting up a planned trip to the FDA in the first half of 2027. The latest result came from Azure-4, where the company met the primary endpoint in untreated patients with substantial hepatitis B burden.

The readout matters because Mirum is entering a market that is no longer theoretical. Gilead Sciences won FDA approval in May for Hepcludex in chronic hepatitis D, so brelovitug is now being framed less as a category-creation story than as a bid to compete on efficacy, dosing and the kinds of patients included in the trials.

The data

In Azure-4, 59% of patients who self-administered a weekly 300 mg injection of brelovitug achieved the combined endpoint of virologic response and aminotransferase (ALT) normalization after 24 weeks. In the monthly 900 mg arm, 44% of patients reached the same endpoint. No patients in a third arm that did not receive brelovitug treatment during the 12 weeks met the endpoint.

The study enrolled 113 patients who had not previously been treated for the disease. According to Fierce Biotech, more than half had cirrhosis and high levels of viral RNA, and the group’s average ALT levels were well above normal. That severity profile could matter commercially if regulators and prescribers view the dataset as relevant to patients who are harder to treat.

Brelovitug works by binding to the hepatitis B antigen, which also exists on the delta form of the virus. Hepatitis D is described in the source report as the most severe form of the disease and affects as many as 4% of patients who also have hepatitis B.

The Azure-4 data followed Azure-1, another phase 3 study that read out in September. In that earlier trial, Mirum also hit the primary endpoints of virologic response and ALT normalization using the same doses and administration timelines. Azure-1 produced virologic response rates of 56% in the 300 mg cohort and 45% in the 900 mg cohort.

The commercial picture

Gilead’s Hepcludex is the clearest benchmark in the market because it already has an FDA nod. Fierce Biotech reported that Hepcludex is a daily injectable treatment with a 48% response rate on the combined endpoint of response rate and ALT normalization. The same report said Hepcludex is approved for patients with chronic hepatitis D without cirrhosis, creating a possible opening for Mirum if brelovitug’s data in a population where more than half had cirrhosis holds up as a meaningful point of differentiation.

The regimen could also be part of the pitch. Azure-4 tested weekly 300 mg self-administration and monthly 900 mg dosing, which gives Mirum flexibility in how it positions the asset against a daily injectable competitor. The weekly arm delivered the strongest efficacy result in the study, making it the most obvious anchor for launch planning.

Competition is still building. Fierce Biotech noted that Vir Biotechnology is running a phase 3 trial combining elebsiran and tobevibart in hepatitis D. Leerink analysts had previously identified Mirum’s enrollment of severe patients as “a key point of differentiation” versus Vir’s combination and also cited low rates of flu-like symptoms as another edge.

The road here

Mirum acquired brelovitug through its $620 million purchase of Bluejay Therapeutics last year. The asset already carries breakthrough designation from the FDA for chronic hepatitis D and orphan drug designation for active hepatitis D.

The company said it plans to take the brelovitug results to the FDA in the first half of 2027 and is aiming for a commercial launch by the end of the year. Alongside the phase 3 package, Mirum is also running mid-stage studies out to 48 weeks and 108 weeks. That longer-term follow-up may matter because the company said deeper responses have been observed with extended treatment in phase 2 work.

The signal from Azure-4 is that Mirum is no longer relying on a single positive study to support its filing strategy. Two phase 3 wins in the same indication, combined with an already approved competitor that has helped define the regulatory path, make brelovitug look more like a launch preparation story than a binary clinical gamble.