Mirum drug eases severe itching in rare liver disease trial

Severe itching eased enough in Mirum Pharmaceuticals’ mid-stage trial to clear a key hurdle for patients with primary sclerosing cholangitis, a rare liver disease that can drive bile buildup, liver damage and, eventually, liver failure. Mirum said volixibat met its primary endpoint in the VISTAS Phase 2b study, cutting itch scores by 1.64 points more than placebo with a p-value below 0.0001.

For people living with PSC, that matters well beyond the mechanics of a trial readout. Cholestatic pruritus can be relentless and debilitating, stealing sleep, concentration and day-to-day function. Recent review literature describes PSC as a rare autoimmune disease marked by biliary strictures, chronic cholestasis and progressive liver dysfunction, and patient advocates say there are no FDA-approved medications to treat or cure it.

Mirum’s study was randomized, double-blind and placebo-controlled. ClinicalTrials.gov lists the trial as starting on December 18, 2020, with actual enrollment of 182 patients, an estimated primary completion date in June 2026 and final study completion in April 2027. Mirum said the main analysis centered on 111 patients with moderate to severe itching, while 47 patients with mild itching were examined separately. In the core group, itch scores fell by 2.72 points from baseline in the volixibat arm, compared with 1.08 points for placebo.

The result is encouraging, but it does not settle the harder questions that determine whether a drug becomes a standard treatment. A mid-stage win does not establish durable benefit over time, nor does it prove the drug will alter the underlying course of PSC. It does, however, suggest that a symptom once considered difficult to move may be meaningfully reduced in a population with few options.

Mirum said the safety profile was generally consistent with IBAT inhibition, with gastrointestinal adverse events and elevations in liver labs including ALT and bilirubin. That profile will matter as regulators weigh whether the benefit on itching outweighs the risks in a chronic disease population that may need long-term treatment.

The company, based in Foster City, California, said a pre-NDA meeting with the U.S. Food and Drug Administration is planned for summer 2026, with a filing expected in the second half of the year. Mirum also said full results will be presented at the European Association for the Study of the Liver International Liver Congress on May 30, 2026. If the data hold up, volixibat could move from a niche trial result to the first targeted therapy for one of PSC’s most punishing symptoms.