Mirum pharmaceutical is on a hot streak. On the heels of an FDA approval and a phase 3 win in hepatitis delta, the rare disease company just announced another phase 3 victory for Livmarli, its ileal bile acid transporter (IBAT) inhibitor.
Mirum’s Expand trial tested Livmarli in patients aged 6 months or older with cholestatic pruritus, an intense itch caused by an ultra-rare cholestatic liver disease. The topline readout showed the trial met its primary endpoint achieved significance across all five secondary endpoints.
The trial included 52 patients, including 46 children and six adults, who received Livmarli or placebo for 20 weeks. Livmarli significantly improved pruritus, generating a 1.81-point improvement in average worst-daily ItchRO(Obs) itch severity score compared to a 0.83 improvement with placebo. Livmarli also reduced baseline serum bile acids by 70.1% compared to 3.5% for the placebo.
In the subgroup of patients with biliary atresia, a rare and life-threatening infant liver condition caused by blocked bile ducts, Livmarli reduced itch severity score by 2.16 points compared to 1.01 in the placebo. The treatment also increased the days with pruritus improvement to 96.4% compared to 52.2% in the placebo group.
Safety data from the trial was consistent with previous Livmarli clinical trials, with no new safety signals, according to Mirum.
“Cholestatic pruritus can be relentless and profoundly disruptive for people living with ultra-rare cholestatic liver diseases, yet treatment options remain limited,” said Jennifer Vittorio, M.D., associate professor of pediatrics and medical director of pediatric liver transplantation at NYU Langone Health. “The magnitude and consistency of improvements in pruritus and serum bile acid levels observed in Expand are compelling, including for patients with biliary atresia.”
Livmarli is already approved by the FDA to treat cholestatic pruritus in two other pediatric cholestatic liver diseases: Alagile syndrome in patients 3 months and older and progressive familial intrahepatic cholestatis (PFIC) for those 12 months and older. Mirum said it plans to file an FDA application to expand Livmarli’s label in the first half of 2027.
The drug was initially flagged as a potential blockbuster in 2014, when Shire paid $260 million to acquire the medicine. Mirum bought the rights to the drug in 2018. And in 2025, the Bay Area pharma reported $360 million in Livmarli sales, a 69% increase over its 2024 sales, suggesting the treatment is on its way to that billion-dollar threshold.
A third indication would also give the drug an edge over its chief competitor and fellow IBAT inhibitor, Bylvay by Ipsen, which only carries two pruritus indications.
The winning readout is just the latest in a series of boosts to Mirum’s pipeline momentum. In August, the drugmaker secured an FDA approval for the rare bone-lesion disorder fibrodysplasia ossificans progressiva (FOP). In September, monoclonal antibody Brelovitug produced positive topline results against hepatitis delta in the phase 3 Azure-1 trial, and Mirum expects the phase 3 Azure-4 results to readout by the end of the year.
Earlier this year, in May, Mirum also saw progress on its pruritus pipeline. Its investigational volixibat secured Breakthrough Therapy and Orphan Drug Designation from the FDA for the treatment of cholestatic pruritus due to primary sclerosing cholangitis (PSC) following a phase 2 win. Mirum expects topline results from the phase 2b trial in the first quarter of 2027.