Mirum Pharmaceuticals, Inc. 8-K

What Happened
Mirum Pharmaceuticals announced on April 27, 2026 that the primary endpoint was met in the Phase 2b portion of the AZURE-1 study of brelovitug, an investigational monoclonal antibody targeting hepatitis B surface antigen (HBsAg) for chronic hepatitis delta virus (HDV). The announcement covers the first patients evaluated at Week 24. At Week 24, brelovitug demonstrated strong antiviral activity: 100% virologic response in the 300 mg once-weekly (QW) arm and 75% in the 900 mg once-every-4-weeks (Q4W) arm, versus 0% in the delayed treatment arm. The composite primary endpoint (virologic response + ALT normalization) was achieved in 45% (300 mg QW) and 35% (900 mg Q4W) of patients versus 0% in delayed treatment; p-values vs delayed treatment were 0.003 and 0.024, respectively. Full Phase 2b results will be presented in a late-breaking poster at the EASL Congress (May 27–30, 2026).

Key Details

• Study snapshot (Week 24, first cohort): efficacy full analysis set n by arm — 300 mg QW: n=20; 900 mg Q4W: n=20; delayed treatment: n=12. The filing references the first 53 patients evaluated at Week 24.
• Virologic response (≥2 log10 HDV RNA reduction or TND): 100% (300 mg QW), 75% (900 mg Q4W), 0% (delayed). HDV RNA <LLOQ/TND: 30% (300 mg QW), 5% (900 mg Q4W), 0% delayed.
• ALT normalization: 45% (300 mg QW), 40% (900 mg Q4W), 8% (delayed). Primary composite endpoint: 45% and 35% vs 0% delayed.
• Safety: generally well tolerated. Any adverse events: 52% (11/21) in 300 mg QW, 50% (10/20) in 900 mg Q4W, 25% (3/12) delayed. Treatment-related AEs: 33% and 35%. No treatment-related Grade 3+ AEs or discontinuations; one Grade 3 musculoskeletal pain (not related) and one hospitalization for cirrhosis (not related, resolved). Injection-site reactions: 14% and 20%.
• Next milestones: full Phase 2b poster at EASL (May 27–30, 2026); topline Phase 3 AZURE-1 and AZURE-4 data expected H2 2026; potential BLA submission and U.S. commercial launch in 2027 (forward-looking).

Why It Matters
These Week 24 results show notable antiviral and liver enzyme improvements with brelovitug versus delayed treatment in a small Phase 2b cohort, supporting its potential as a single-agent therapy for HDV. For investors, the data establish clinical proof-of-concept ahead of planned Phase 3 readouts (H2 2026) and potential regulatory filings in 2027. The filing also notes tolerability was acceptable in the limited cohort, but larger Phase 3 data will be key to confirm efficacy and safety before any approval or commercial decision.