Mirum Pharmaceuticals (MIRM) Study result summary

Study design

• Phase 3 EXPAND randomized 52 patients, including 46 pediatric and six adults, to maralixibat 285 μg/kg twice daily or placebo for 20 weeks, followed by a 20-week open-label extension.

• The FDA-aligned cross-disease trial enrolled patients with moderate-to-severe pruritus across ultra-rare cholestatic liver diseases; efficacy analyses included 46 children and 25 with biliary atresia, and the safety population included 52.

Efficacy results

• Primary endpoint met: pediatric pruritus severity improved 1.81 points with maralixibat vs 0.83 with placebo; placebo-adjusted difference 0.98 points (p=0.0004).

• Serum bile acids fell 70.1% from baseline with maralixibat vs 3.5% with placebo; treatment effect was 69.0% (p<0.0001).

• All five prespecified secondary endpoints were met; pruritus improvement days were 86.0% with maralixibat vs 49.1% with placebo in pediatric patients (treatment effect 36.9%; p=0.0008).

• ~80% of the overall population achieved at least a 1-point pruritus improvement.

Biliary atresia subgroup

• In patients with biliary atresia and a native liver, pruritus severity improved 2.16 points with maralixibat vs 1.01 with placebo; treatment difference 1.15 points (p=0.0002).

• Pruritus improvement days were 96.4% vs 52.2% (p=0.0045); serum bile acids fell 75.5% vs 9.0%, a treatment effect of 73.1% (p<0.0001).

• ~90% of biliary atresia patients achieved at least a 1-point pruritus improvement; effects were consistent with other cholestatic liver diseases studied.

• Addressable population estimated at 1,000 U.S. patients and 2,000 across the U.S. and Europe: patients post-Kasai with a native liver and pruritus.