Mirum reports positive Phase 2b PSC itch data for volixibat: full analysis

Mirum Pharmaceuticals has reported a positive Phase 2b readout for volixibat in primary sclerosing cholangitis, a rare cholestatic liver disease with no approved drug therapy. In the VISTAS study, the investigational oral IBAT inhibitor met its primary endpoint in PSC patients with cholestatic pruritus, with Mirum positioning the asset as a potential first approved treatment for itch in this population. (biospace.com)

The update has been a long time coming. Mirum first announced the VISTAS study in January 2021 as a randomized, double-blind, placebo-controlled Phase 2b trial in adults with PSC, designed not only to assess itch reduction, but also safety, quality of life, serum bile acids, and exploratory markers of disease progression. Enrollment completion was announced in September 2025, and as recently as early 2026 the company had been guiding investors to expect topline data in the second quarter of 2026. (ir.mirumpharma.com)

According to Mirum’s announcement, the primary analysis cohort showed a 2.72-point improvement from baseline in pruritus on the Adult ItchRO scale for volixibat, compared with a 1.08-point improvement for placebo, a placebo-adjusted difference of 1.64 points with a p value below 0.0001. The company said statistically significant itch improvement emerged within two weeks and was also seen in a secondary cohort of patients with milder baseline itch. Safety was described as generally consistent with the IBAT class, led mainly by gastrointestinal adverse events and elevations in ALT and bilirubin. In pooled primary and secondary cohorts, treatment-emergent adverse events occurred in 93.5% of volixibat-treated patients and 84.0% of placebo patients; serious adverse events occurred in 10.4% and 6.2%, respectively; and study discontinuation due to diarrhea was reported in 3.9% versus 1.2%. (biospace.com)

The broader context matters here. PSC is a chronic, progressive biliary disease associated with inflammation, fibrosis, recurrent cholangitis, malignancy risk, and eventual liver failure. About 70% of patients also have inflammatory bowel disease, most often ulcerative colitis. Current guidance emphasizes that there is still no effective medical therapy proven to alter transplant-free survival in PSC, while itch management remains piecemeal and often unsatisfactory, relying on older approaches such as bile acid sequestrants, rifampin, opioid antagonists, or fibrates depending on region and guideline. (ir.mirumpharma.com)

Mirum and outside stakeholders are framing the result as meaningful because pruritus is one of the disease’s most disruptive symptoms. In the company’s release, investigator Kris Kowdley said PSC remains challenging to manage and that clinicians have very limited options to effectively address itch. PSC Partners Seeking a Cure also highlighted the trial result for the patient community, underscoring how central itch is to day-to-day burden. Those reactions fit with the wider literature, which describes cholestatic pruritus as under-recognized, undertreated, and highly consequential for sleep, functioning, and quality of life. (biospace.com)

Why it matters: For veterinary professionals, this is primarily a human drug-development story, but it’s relevant as a window into how bile acid biology is being leveraged to manage refractory itch in cholestatic disease. Mirum already has deep experience in this mechanism through its IBAT portfolio, and the VISTAS result strengthens the case that symptom-directed endpoints such as pruritus can support meaningful regulatory conversations in rare hepatobiliary disorders. It also reinforces a broader industry trend: companies are increasingly targeting quality-of-life burdens, not just hard hepatic outcomes, when diseases are slow-moving and difficult to study. (biospace.com)

What to watch: The next inflection points are close. Full VISTAS data are scheduled for a late-breaking oral presentation at EASL on May 30, 2026, which should give clinicians a better look at subgroup performance, durability, and the safety profile. Mirum has said a pre-NDA meeting with the FDA is planned for summer 2026, with a U.S. filing expected in the second half of 2026. Investors and clinicians will also be watching whether the company can replicate momentum across its broader volixibat program, with topline data from the VANTAGE study in primary biliary cholangitis now expected in the first quarter of 2027. (nasdaq.com)