Mirum Pharmaceuticals Inc. (MIRM), a rare diseases company, announced that the primary endpoint was met in the VISTAS Phase 2b study evaluating Volixibat for the treatment of primary sclerosing cholangitis (PSC). Primary sclerosing cholangitis (PSC) is a rare, serious, idiopathic chronic cholestatic liver disease characterised by cholestasis, progressive inflammation, and destruction of bile ducts, which may lead to fibrosis, cirrhosis, portal hypertension, cancer, and ultimately liver failure.
Mirum's lead investigational candidate, Volixibat, is being developed as an orally administered, minimally absorbed inhibitor of IBAT, a protein that recycles bile acids from the intestines to the liver.
Trial Details
The Phase 2b VISTAS trial is a global, randomised, double-blind, placebo-controlled study evaluating the safety and efficacy of Volixibat in the treatment of PSC.
The VISTAS Phase 2b study included 158 patients with PSC who were assigned to either a primary analysis cohort of moderate to severe itch (n=111) or a secondary analysis cohort of mild itch (n=47) based on baseline itch severity, as measured by the Adult Itch Reported Outcome (ItchRO) scale.
The primary endpoint is a reduction in pruritus as measured by the Adult ItchRO, a pruritus numerical rating scale ranging from 0 (no itch) to 10 (worst possible itch). The study completed a blinded interim analysis in 2024 and established the efficacy threshold at 20 mg BID.
Key Findings
In the primary analysis cohort, treatment with Volixibat demonstrated a robust 2.72-point improvement in Pruritus and a placebo-adjusted difference of 1.64 points in the primary endpoint, as measured by the Adult ItchRO scale, reflecting change from baseline to the average of the last 12 weeks of treatment.
In addition, the firm noted that statistically significant improvements in pruritus were observed within two weeks of treatment and were also observed in the secondary cohort of patients with mild itch at baseline.
Volixibat's safety profile was generally consistent with the known effects of IBAT inhibition, primarily gastrointestinal adverse events and some elevations in liver tests, according to the firm.
The company is also studying Volixibat for the treatment of primary biliary cholangitis (PBC) in the ongoing Phase 2 VANTAGE trial.
Mirum has a pre-New Drug Application (NDA) meeting with the FDA for Volixibat in PSC scheduled for the summer of 2026, with a planned NDA submission in the second half of 2026.
"These results mark an important milestone for the PSC community, where there are currently no approved therapies," said Joanne Quan, M.D., Chief Medical Officer at Mirum.
MIRM has traded between $40.00 and $110.49 over the last year. The stock closed Friday's trade at $96.53.
MIRM is currently up 13.90%, at $110.15.
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