Mirum Pharmaceuticals, Inc. 8-K

What Happened

• On May 4, 2026 Mirum Pharmaceuticals announced the VISTAS Phase 2b study of volixibat (20 mg BID), an oral IBAT inhibitor, met its primary endpoint in patients with primary sclerosing cholangitis (PSC).
• The trial enrolled 158 patients split into a primary analysis cohort (moderate–severe itch, n=111) and a secondary cohort (mild itch, n=47). In the primary cohort (volixibat n=54; placebo n=57), the model‑adjusted (LS) mean change in Adult ItchRO was –2.72 for volixibat vs –1.08 for placebo, a placebo‑adjusted difference of –1.64 (p<0.0001). A ≥2‑point reduction in ItchRO occurred in 55.6% of volixibat patients vs 26.3% on placebo (difference 29.3%, p=0.0019). Serum bile acids (sBA) fell (LS mean –33.7 µmol/L vs +2.1 µmol/L; difference –35.8, p=0.0324).
• Safety: adverse events were mainly gastrointestinal and liver‑related. Any treatment‑emergent AE occurred in 93.5% (volixibat) vs 84.0% (placebo); serious TEAEs were 10.4% vs 6.2%; TEAEs leading to study discontinuation were 9.1% vs 2.5%. Diarrhea was the most common AE (40.3% volixibat vs 8.6% placebo).

Key Details

• Filing date / announcement: May 4, 2026.
• Primary analysis cohort results: LS mean ItchRO change –2.72 (volixibat) vs –1.08 (placebo); between‑group difference –1.64, p<0.0001.
• Safety snapshot (combined cohorts): TEAEs any 93.5% (VLX, N=77) vs 84.0% (PBO, N=81); discontinuations for TEAEs 9.1% vs 2.5%; diarrhea 40.3% vs 8.6%.
• Next regulatory/clinical milestones: pre‑NDA meeting with FDA scheduled summer 2026; planned NDA submission in H2 2026; full results to be presented at EASL on May 30, 2026. Topline VANTAGE (PBC) Phase 2b data expected Q1 2027.

Why It Matters

• The positive Phase 2b itch results support volixibat as a potential first treatment for cholestatic pruritus in PSC, a symptom with limited approved options. Statistically significant and clinically meaningful itch reduction and sBA lowering are key efficacy signals investors watch for regulatory approval.
• Safety signals (notably GI events and increases in liver labs) are material and will be important in FDA discussions and labeling considerations. The company’s planned pre‑NDA meeting and H2 2026 NDA target create a clear near‑term regulatory timeline for investors to follow.
• Upcoming public presentation (EASL May 30) and the PBC trial readout in Q1 2027 provide additional catalysts and datapoints for assessing volixibat’s commercial and regulatory prospects.