FOSTER CITY, Calif., May 4, 2026
Mirum Pharmaceuticals, Inc. has announced that its Phase 2b VISTAS clinical study of volixibat successfully met its primary endpoint, demonstrating statistically significant and clinically meaningful reductions in cholestatic pruritus in patients with primary sclerosing cholangitis (PSC). This milestone represents a major advancement in rare liver disease therapeutics, as PSC currently has no approved treatment options, highlighting the potential of volixibat as a first-in-class therapy.
Phase 2b Data Demonstrates Strong Clinical Efficacy
The VISTAS Phase 2b study, a global randomized, double-blind, placebo-controlled trial, evaluated 158 patients with PSC, focusing on the reduction of cholestatic pruritus, one of the most debilitating symptoms of the disease. Patients treated with volixibat achieved a 2.72-point reduction from baseline in itch severity, with a placebo-adjusted improvement of 1.64 points (p<0.0001), confirming both statistical significance and clinical relevance.
Importantly, rapid onset of efficacy was observed, with improvements in pruritus reported within two weeks of treatment, and consistent benefits seen across both moderate-to-severe and mild patient cohorts. Additionally, more than 55% of patients achieved a ≥2-point reduction in itch severity, significantly outperforming placebo. These results underscore the potential of volixibat to directly address a core symptom burden that severely impacts patient quality of life.
Mechanism of Action Targets Bile Acid Pathway
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Volixibat is an oral ileal bile acid transporter (IBAT) inhibitor, designed to reduce bile acid reabsorption in the intestine, thereby lowering systemic bile acid levels and hepatic accumulation, which are key drivers of pruritus in cholestatic liver diseases. By targeting this pathway, volixibat offers a novel, mechanism-based therapeutic approach for PSC, differentiating it from existing symptomatic treatments.
The safety profile observed in the trial was consistent with the known pharmacology of IBAT inhibition, with the most common adverse events being gastrointestinal effects and liver enzyme elevations, generally manageable and expected in this class of therapy. Importantly, no new safety signals were identified, supporting continued clinical development and regulatory progression.
Regulatory Pathway and Future Development Plans
Following the successful Phase 2b results, Mirum has scheduled a pre-New Drug Application (NDA) meeting with the U.S. FDA in summer 2026, with plans to submit an NDA in the second half of 2026, marking a critical step toward potential regulatory approval. Full clinical data from the VISTAS study will be presented at the European Association for the Study of the Liver (EASL) International Liver Congress 2026, further validating the findings within the global scientific community.
In addition to PSC, volixibat is also being evaluated in primary biliary cholangitis (PBC) through the ongoing VANTAGE Phase 2b study, with topline data expected in 2027. The therapy has already received FDA Breakthrough Therapy designation for PBC, reinforcing its potential as a high-impact treatment in cholestatic liver diseases.
Implications for Rare Disease and Liver Therapeutics
The success of the VISTAS study highlights the importance of targeted therapies in rare and underserved diseases, where unmet medical need remains high. PSC affects approximately 30,000 patients in the United States, with symptoms such as chronic itching, fatigue, and liver dysfunction significantly impairing quality of life and often leading to liver transplantation or cancer risk.
Volixibat’s ability to deliver rapid, sustained symptom relief positions it as a potential first approved therapy for PSC, which could transform the treatment landscape and improve outcomes for patients with limited options. This development also reinforces the broader trend in biopharmaceutical innovation, where precision-targeted mechanisms and strong clinical validation are driving progress in complex diseases.
Source: Mirum press release
