Mirum Pharmaceuticals Announces Primary Endpoint Met in Phase 3 AZURE-1 Study of Brelovitug in Chronic Hepatitis Delta Virus

– Phase 3 primary endpoint (virologic response and ALT normalization) achieved in both dose arms at Week 24– 48-week data from Phase 2b portion of AZURE-1 demonstrate deepening viral suppression and increased rates of ALT normalization with longer-term treatment– Favorable safety and tolerability profiles observed; no new safety signals– Mirum to host conference call to discuss topline results today, September 28, at 8:30 a.m. ET

Mirum Pharmaceuticals, Inc. (Nasdaq: MIRM), a leading rare disease company, today announced the primary endpoint was met in the Phase 3 portion of the AZURE-1 study evaluating brelovitug, an investigational fully human monoclonal antibody that binds to hepatitis B surface antigen (HBsAg), for the treatment of chronic hepatitis delta virus (HDV). In addition, 48-week data from the Phase 2b portion of AZURE-1 demonstrated deepening viral suppression, with a greater proportion of patients achieving HDV RNA below the lower limit of quantification (LLOQ, <10 IU/mL) and target not detected (TND), and increased rates of alanine aminotransferase (ALT) normalization. AZURE-1 is one of two pivotal Phase 3 studies intended to form the basis of Mirum’s U.S. registration package for brelovitug.

“These results demonstrate the potential of brelovitug as a well-tolerated, convenient, single agent to deliver both deep viral suppression and ALT normalization, with responses that continue to deepen through 48 weeks of treatment. Notably, these results were achieved in a broad patient population, including those with significant liver inflammation, cirrhosis and clinically significant portal hypertension,” said Nancy Shulman, M.D., Executive Vice President of Clinical Development at Mirum. “We look forward to reporting topline results from AZURE-4 later this year and advancing toward our planned BLA submission in the first half of 2027.”

“The goal of treating chronic HDV is to prevent progression to cirrhosis, liver cancer and liver failure, and that requires controlling both the virus and liver inflammation,” said Norah Terrault, M.D., MPH, Professor of Medicine and Chief of the Division of GI and Liver at the Keck School of Medicine of USC, and an AZURE-1 investigator. “ALT is a marker of liver injury, so seeing virologic response alongside ALT normalization is encouraging in a long-term therapy. For patients facing the most aggressive form of viral hepatitis, these are important results.”

“Chronic hepatitis delta is a lifelong disease, and people living with it need treatment options that are effective, safe and tolerable enough to stay on over time. That’s especially true for patients with more advanced disease, who often have the fewest choices,” said Chari A. Cohen, DrPH, MPH, President of the Hepatitis B Foundation. “Results like these bring hope to a community that has had few options until recently.”

Phase 3 AZURE-1 Results: Brelovitug Met the Primary Endpoint at Week 24

The Phase 3 portion of the AZURE-1 study enrolled 153 treatment-naive patients randomized in a 2:2:1 ratio to receive brelovitug 300 mg self-administered once weekly (QW) by subcutaneous (SC) injection, brelovitug 900 mg administered once every four weeks (Q4W) by SC injection, or delayed treatment starting at Week 24. This global study enrolled a broad patient population including patients with advanced disease.

At Week 24, treatment with brelovitug met the primary endpoint, with 56% of patients in the 300 mg QW arm and 45% in the 900 mg Q4W arm achieving the combined endpoint of virologic response (≥2 log10 reduction in HDV RNA from baseline or undetectable HDV RNA [<LLOQ, TND]) and ALT normalization, compared to 0% in the delayed treatment arm (p<0.0001 for both comparisons). The efficacy results by treatment arm at Week 24 are presented below in Phase 3 Key Efficacy Endpoints.

Treatment with brelovitug was well tolerated across dose groups, with a safety profile consistent with previously reported AZURE-1 data. The safety profile summary is presented below in Phase 3 Summary of Safety Through Week 24.

48-Week Data from the Phase 2b Portion of AZURE-1: Deepening Viral Suppression and Increased Rates of ALT Normalization

The Phase 2b portion of AZURE-1 included the first 53 patients enrolled in the study. Following the previously reported Week 24 primary analysis, patients continued treatment in the open-label extension. Between Week 24 and Week 48, viral suppression deepened and rates of ALT normalization increased. The Week 48 results are presented below in Phase 2b Key Efficacy Endpoints (Weeks 24 and 48).

Safety in the Phase 2b portion through Week 48 was consistent with previously reported results, with no new safety signals observed.

The full results from the Phase 3 AZURE-1 study will be presented at an upcoming medical congress. Topline results from the Phase 3 AZURE-4 study, the second of the two pivotal studies supporting the U.S. registration package, are expected in Q4 2026. Mirum expects to submit a Biologics License Application (BLA) to the U.S. Food and Drug Administration (FDA) in H1 2027, with potential commercial launch in the U.S. in Q4 2027.

Conference Call to Discuss AZURE-1 Topline Results

Mirum will host a conference call today, Monday, September 28, at 8:30 a.m. ET to share topline results from the Phase 3 AZURE-1 study of brelovitug in HDV, along with 48-week data from the Phase 2b portion of the study. Join the call using the following details:

Conference Call Details:

US/Toll-Free: +1 833 461 5787
International: +1 585 542 9983
Access Code: 979912911

You may also access the call via webcast by visiting the Investors section of Mirum’s corporate website. The archived webcast will be available for replay.

About Chronic Hepatitis Delta Virus (HDV)

HDV, an infection that occurs in some people infected with the hepatitis B virus, is the most severe form of viral hepatitis due to the potential for rapid progression to liver cirrhosis, liver cancer, and liver-related death. HDV affects approximately 230,000 people in the United States and Europe. It is estimated that more than 50% of individuals with HDV will die of liver-related causes within 10 years of diagnosis. There are currently no approved treatments for HDV in the United States and in most countries worldwide.

About Brelovitug

Brelovitug is an investigational, highly potent, pan-genotypic, fully human immunoglobulin G1 (IgG1) monoclonal antibody (mAb) that targets the surface antigen (anti-HBsAg) on both the hepatitis delta virus (HDV) and the hepatitis B virus (HBV). Brelovitug is designed to neutralize and remove hepatitis B and hepatitis D virions and deplete HBsAg-containing subviral particles. Brelovitug has FDA Breakthrough Therapy designation for the treatment of chronic HDV and PRIME and Orphan designations from the European Medicines Agency.

In April 2026, Mirum announced that in the Phase 2b portion of the AZURE-1 study, treatment with brelovitug demonstrated strong antiviral activity in HDV and achieved the primary combined endpoint of virologic response and alanine aminotransferase (ALT) normalization at Week 24 in both brelovitug dose arms as compared to the delayed treatment arm. Favorable safety and tolerability profiles were observed. Brelovitug is currently being evaluated in the global Phase 3 AZURE clinical program. Mirum owns worldwide rights to brelovitug.

About the AZURE Clinical Program

The AZURE program is a global, registrational Phase 3 clinical development program evaluating brelovitug for the treatment of chronic hepatitis delta virus (HDV). The program includes multiple open-label studies designed to assess the primary endpoint of combined virologic response and ALT normalization. Together, the studies are intended to support regulatory filings in the United States and Europe.

About AZURE-1

AZURE-1 is a Phase 2b/3 study evaluating brelovitug in chronic hepatitis delta virus (HDV). The study has enrolled approximately 200 treatment-naive patients randomized in a 2:2:1 ratio to receive brelovitug 300 mg self-administered once weekly (QW) by subcutaneous (SC) injection, brelovitug 900 mg administered once every four weeks (Q4W) by SC injection, or 24-week delayed therapeutic start. Patients randomized to delayed treatment initiate brelovitug 300 mg once weekly upon completion of the treatment delay in the study. The Phase 2b portion of the study included the initial approximately 50 patients enrolled, with a prespecified safety and efficacy analysis conducted upon availability of 24-week data from that cohort.

The primary endpoint of the study is the proportion of patients achieving combined virologic response and ALT normalization at Week 24 and includes open-label extension periods of up to 96 weeks.

About Mirum Pharmaceuticals

Mirum Pharmaceuticals (NASDAQ: MIRM) is a leading rare disease company with a global footprint of approved products and a broad pipeline of investigational medicines. Purpose-built to bring forward breakthrough medicines for people with overlooked conditions, Mirum focuses on rare liver and rare genetic diseases, where it has built deep expertise and strong connections to patient communities. The company’s commercial portfolio includes LIVMARLI^® (maralixibat) for Alagille syndrome (ALGS) and progressive familial intrahepatic cholestasis(PFIC),ATEBRIOZ™ (zilurgisertib) for fibrodysplasia ossificans progressiva (FOP), CHOLBAM^® (cholic acid) for bile-acid synthesis disorders and CTEXLI^® (chenodiol) for cerebrotendinous xanthomatosis (CTX).

Mirum’s clinical-stage pipeline includes volixibat, an IBAT inhibitor in late-stage development for primary sclerosing cholangitis (PSC) and primary biliary cholangitis (PBC), brelovitug, a fully human monoclonal antibody in late-stage development for chronic hepatitis delta virus (HDV) and MRM-3379, a PDE4D inhibitor being evaluated for Fragile X syndrome (FXS).

Mirum’s success is driven by a team dedicated to advancing high impact medicines through strategic development, disciplined execution and purposeful collaboration across the rare disease ecosystem. Learn more at www.mirumpharma.com and follow Mirum on Facebook, LinkedIn, Instagram and X.

Forward-Looking Statements

Statements contained in this press release regarding matters that are not historical facts are “forward-looking statements” within the meaning of the Private Securities Litigation Reform Act of 1995. Such forward-looking statements include statements regarding, among other things, the expected timing of topline data for the AZURE studies and potential BLA submission and commercial launch, the potential benefits of brelovitug, the relationship of antiviral activity as an important endpoint in HDV and the success or approval of any potential regulatory submission for brelovitug. Because such statements are subject to risks and uncertainties, actual results may differ materially from those expressed or implied by such forward-looking statements. Words such as “anticipate,” “expected,” “will,” “could,” “would,” “potential,” “continue,” “plans,” “intended,” “believe,” and similar expressions are intended to identify forward-looking statements. These forward-looking statements are based upon Mirum’s current expectations and involve assumptions that may never materialize or may prove to be incorrect. Actual results could differ materially from those anticipated in such forward-looking statements as a result of various risks and uncertainties, which include, without limitation, risks and uncertainties with the development of investigational medicines generally, including the failure of future studies to generate the same or similar data as prior studies and the potential that estimated prevalences are materially inaccurate; the risks and uncertainties associated with Mirum’s business in general, the impact of geopolitical and macroeconomic events, and the other risks described in Mirum’s Quarterly Report on Form 10-Q for the quarter ended June 30, 2026, filed with the Securities and Exchange Commission on August 5, 2026, and subsequent filings with the Securities and Exchange Commission, which are available at www.sec.gov. All forward-looking statements contained in this press release speak only as of the date on which they were made and are based on management’s assumptions and estimates as of such date. Mirum undertakes no obligation to update such statements to reflect events that occur or circumstances that exist after the date on which they were made, except as required by law.

Mirum and the Mirum logo are trademarks of Mirum Pharmaceuticals, Inc.

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