Brelovitug Phase 3 Readout: Validated Pathway, Unknown Data, Harder Payer Bar

Mirum to Share Topline Brelovitug Phase 3 AZURE-1 Results

Mirum Pharmaceuticals, Inc. announced it will host an investor call on Monday, September 28, 2026, to present topline results from its Phase 3 AZURE-1 study of brelovitug for chronic hepatitis delta virus (HDV). The call will also include 48-week data from the Phase 2b portion of the study. This event is significant for the rare disease company as it progresses its late-stage pipeline, particularly in rare liver diseases, reinforcing its commitment to developing breakthrough medicines for overlooked conditions.

• Mirum Pharmaceuticals is preparing to unveil crucial clinical data for its investigational drug, brelovitug, in chronic hepatitis delta virus (HDV). The company has scheduled an investor call for September 28, 2026, to disclose the topline results from the pivotal Phase 3 AZURE-1 study, marking a significant milestone in the drug's development pathway.
• Beyond the primary Phase 3 AZURE-1 topline results, the investor call will also feature an update on the longer-term efficacy and safety profile of brelovitug. Specifically, 48-week data from the Phase 2b portion of the study will be shared, providing a more comprehensive view of the drug's performance over an extended period.
• Mirum Pharmaceuticals positions itself as a leader in rare diseases, with a particular emphasis on rare liver and rare genetic conditions. The advancement of brelovitug, a fully human monoclonal antibody, for chronic HDV aligns with the company's core strategy of developing breakthrough medicines for overlooked conditions and expanding its global footprint in this specialized therapeutic area.

Addressing the Unmet Needs in Chronic Hepatitis Delta Virus

Chronic hepatitis D (CHD) represents the most severe form of viral hepatitis, characterized by accelerated progression to cirrhosis, increased risk of hepatic decompensation, and heightened incidence of hepatocellular carcinoma (HCC). Despite recent therapeutic advances, significant challenges persist across treatment efficacy, durability, and clinical trial methodology.

• Limited efficacy and high relapse rates with pegylated interferon-alpha (PEG-IFNα): Until the introduction of bulevirtide (BLV), PEG-IFNα stood as the sole available treatment for CHD, despite suboptimal response rates and considerable adverse effects. Sustained virological response (SVR) rates remain low, and relapse is frequent even when SVR is achieved. In a nine-year retrospective analysis, 16 of 19 patients (84.2%) with high baseline HDV RNA levels (>1 × 10⁵) and 10 of 14 patients (71.4%) with high HBsAg titers (>10² IU/mL) relapsed after treatment. A ten-year follow-up of the HIDIT-I trial further confirmed that clinical complications on long-term follow-up were associated with nonresponse to therapy and baseline cirrhosis, with annual event-free survival in cirrhotic patients falling to 35% at year 10 versus 76% in non-cirrhotic patients.

• Uncertainty around bulevirtide treatment duration and stopping rules: EMA recommends proceeding with BLV therapy until proven clinical benefit, without further details on treatment duration. Data on the safety and efficacy of stopping BLV therapy upon long-term HDV-RNA suppression remain scarce. In a small cohort of seven Austrian patients who discontinued BLV, HDV-RNA relapses were observed in four patients during long-term follow-up, and all patients who relapsed had undergone BLV monotherapy. Future studies are needed to define stopping rules and further investigate the safety of stopping BLV.

• Suboptimal response in a substantial proportion of patients on BLV monotherapy: In a nationwide Austrian cohort of 61 patients, 31.1% required add-on pegylated interferon alfa-2a (PEG-IFN) after a median of 10.5 months due to suboptimal response to BLV monotherapy. While add-on PEG-IFN induced a further HDV-RNA decline of 1.65 (IQR 0.81–2.11) log copies/mL and HBsAg reductions of 0.08 (IQR 0.02–0.12) log IU/L after 24 weeks of combined therapy (both p<0.01), management of suboptimal responders remains an active clinical challenge.

• Lack of effective treatment for patients with decompensated disease: Nucleos(t)ide analogue (NA) therapies do not affect CHD despite HBV's close dependency on HBsAg for HDV cellular entry and propagation. BLV's EMA conditional approval in July 2020 was specifically for adult patients with compensated CHD, leaving patients with decompensated liver disease without an approved targeted option.

• Significant variability in clinical trial endpoints and HDV RNA quantification: The optimal way to measure success in HDV clinical trials remains unknown and continues to evolve. Significant variability exists in endpoints used to evaluate therapeutics, including the use of a ≥2-log decline in HDV RNA with or without undetectable serum HDV RNA as a virological response marker. Additionally, significant variability still exists in nucleic acid quantification techniques for HDV RNA, with quantification assays differing in their sensitivity, complicating cross-study comparisons.

• Absence of significant histological benefit across available regimens: A network meta-analysis of 14 randomized controlled trials (814 patients) found that the seven regimens included in the study did not contribute significantly to liver histological improvement, with NAs showing superiority to BLV for histological response (RR = 2.08, 95% CI [1.10, 3.93]) as the only statistically significant histological finding among comparisons.

Unpacking the AZURE-1 Study Design and Key Endpoints

Several pivotal clinical trials have evaluated antiviral therapies for chronic hepatitis delta (CHD), spanning pegylated interferon monotherapy, bulevirtide (BLV) monotherapy, and combination regimens. These studies vary in phase, duration, and endpoint definitions, collectively shaping the current treatment landscape for HDV.

Brelovitug's Potential Role in the Evolving HDV Treatment Landscape

The treatment landscape for chronic hepatitis D (CHD) has undergone substantial evolution, with bulevirtide (BLV) emerging as the most clinically significant advance over the historical standard of care. For decades, pegylated interferon-alpha (PegIFNα) stood as the sole available treatment, despite suboptimal response rates, considerable adverse effects, and high rates of post-treatment relapse. A 2008 analysis confirmed that nucleoside analogues inhibiting HBV are ineffective against HDV, and that combination therapy with lamivudine or ribavirin showed no significant advantages over monotherapy with standard or pegylated interferon. Against this backdrop, BLV — a first-in-class entry inhibitor targeting the sodium taurocholate co-transporting polypeptide (NTCP) receptor — received conditional EMA approval in July 2020 at 2 mg daily, followed by full approval in May 2023, marking a central shift in the therapeutic paradigm.

Head-to-head and network evidence consistently positions BLV, particularly in combination with PegIFNα, above prior standard-of-care regimens. A systematic review and network meta-analysis of 13 studies (n = 922) found that at end of treatment, bulevirtide monotherapy (OR 38.63, p < 0.05) and its combination with PegIFNα (OR 260.08, p < 0.05) significantly suppressed HDV RNA, with the combination achieving the highest suppression of any regimen evaluated. Combined response was also highest with bulevirtide-PegIFNα (OR 112.69, p < 0.05). In the phase 2b MYR 204 trial, at 24 weeks after end of treatment, undetectable HDV RNA was achieved in 46% of patients receiving 10 mg BLV plus PegIFNα versus 12% with 10 mg BLV monotherapy — a between-group difference of 34 percentage points (95% CI, 15 to 50; P<0.001). By contrast, PegIFNα alone achieved undetectable HDV RNA in only 17% at the same timepoint. The phase III MYR301 study further demonstrated that virologic and biochemical responses were maintained and improved with longer-term BLV monotherapy through week 96, with 43% of non-responders and 82% of partial responders at week 24 achieving virologic response by week 96.

Real-world data reinforce the clinical trial findings. In the nationwide Austrian CHD cohort (n = 61, median treatment duration 29.0 months), BLV achieved virological response rates of 36.4% at month 6, 64.2% at month 12, and 61.9% at month 24, alongside significant reductions in liver stiffness and systemic inflammation markers (all p<0.01). Among 19 suboptimal responders who received add-on PegIFNα, a further HDV-RNA decline of 1.65 log copies/mL (IQR 0.81–2.11) and HBsAg reduction of 0.08 log IU/L (IQR 0.02–0.12) were observed after 24 weeks of combined therapy (both p<0.01). The Italian ARISTOTLE pilot study (n = 108) reported a virological response in 54.6% of patients at 6 months, with median HDV RNA dropping from 29,800 IU/mL to 0 IU/mL (p<0.001) and significant ALT and AST normalization among responders. Across both trial and real-world settings, BLV demonstrated a favorable safety profile, with adverse events predominantly mild and no serious adverse events attributed to BLV in the MYR301 study.

Brelovitug's Potential to Reshape Chronic HDV Treatment

The upcoming investor call from Mirum Pharmaceuticals regarding topline Phase 3 AZURE-1 results for brelovitug in chronic hepatitis delta (CHD) marks a critical juncture for patients and the pharmaceutical industry. CHD is recognized as the most severe form of viral hepatitis, driving rapid progression to cirrhosis and liver failure, underscoring a profound unmet medical need. Historically, treatment options have been limited, with interferon therapy offering only modest efficacy in directly suppressing HDV replication.

The landscape has recently evolved with the conditional and full approval of bulevirtide (Myrcludex-B), an entry inhibitor that has demonstrated significant virological and biochemical improvements, even in patients with advanced liver disease and portal hypertension, over treatment periods extending to 96 weeks. This sets a high benchmark for any new entrant.

Mirum's brelovitug, if successful, could offer another vital therapeutic avenue. The presentation of both topline Phase 3 and 48-week Phase 2b data is particularly important. While bulevirtide has shown sustained responses and a manageable safety profile, including mild adverse events like increased bile acids and injection-site reactions, the long-term nature of CHD treatment necessitates continuous monitoring and well-tolerated options. Brelovitug will need to demonstrate not only robust efficacy but also a favorable safety profile that supports prolonged administration, potentially differentiating itself from existing therapies or offering an alternative for patients who may not respond optimally to current treatments. The ability to achieve sustained virological and biochemical responses, particularly in patients with advanced disease or those who are suboptimal early responders, will be key to its clinical adoption and market success. This event will provide crucial insights into whether brelovitug can carve out a significant role in the challenging fight against CHD.