Mirum Pharmaceuticals Inc.

10/13/2026 | Press release | Distributed by Public on 10/13/2026 06:09

Material Event (Form 8-K)

Item 8.01 Other Events.
Announcement of Data from the Phase 3 EXPAND Study of LIVMARLI (maralixibat) in Ultra-Rare Cholestatic Liver Diseases
On October 12, 2026, Mirum Pharmaceuticals, Inc. (the "Company") announced topline results from the Phase 3 EXPAND study evaluating LIVMARLI (maralixibat) ("Livmarli") for the treatment of cholestatic pruritus in patients aged 6 months or older with ultra-rare cholestatic liver diseases, including biliary atresia ("BA"). The study met its primary endpoint and achieved statistical significance across all five prespecified secondary endpoints, including the three endpoints in patients with BA and a native liver.
The Phase 3 EXPAND study enrolled 52 patients, including 46 pediatric and six adult patients, who were randomized during the 20-week double-blind period to treatment with maralixibat 285 µg/kg twice daily ("BID") or placebo.
Treatment with maralixibat demonstrated a statistically significant improvement in pruritus compared with placebo in the primary analysis population of pediatric patients. Maralixibat resulted in a mean 1.81-point improvement from baseline in average worst-daily ItchRO(Obs) severity score during Weeks 13-20 compared with a 0.83-point improvement for placebo, corresponding to a placebo-adjusted treatment difference of 0.98 points (p=0.0004). Maralixibat also resulted in a 70.1% reduction from baseline in serum bile acids ("sBA"), compared with 3.5% for placebo, corresponding to a 69.0% treatment effect versus placebo (p<0.0001). Key efficacy data from the Phase 3 EXPAND study are presented below in the "Efficacy Results" table.
Safety findings in the Phase 3 EXPAND study were consistent with prior clinical experience with maralixibat and no new safety signals were observed. Key safety data from the Phase 3 EXPAND study are presented below in the "Safety Summary" table.
The Company plans to submit a supplemental New Drug Application in the United States in the first half of 2027 based on the Phase 3 EXPAND study results.
Efficacy Results - Primary and Secondary Endpoints
Maralixibat
285 µg/kg BID
 		Placebo Treatment Effect
(MRX-PBO)
 		p-value
OVERALL STUDY ANALYSES
Primary Endpoint: Change in ItchRO(Obs) severity score (SE)b
-1.81 (0.18)a
-0.83 (0.18)a
-0.98 0.0004
All Pediatric Population n=22 n=24
Percentage of days with pruritus improvement 86.0% 49.1% 36.9% 0.0008
All Pediatric Population n=22 n=24
Relative % change from baseline in total sBA -70.1% -3.5%
-69.0%c
<0.0001
Overall Population n=25 n=27
BILIARY ATRESIA (BA) WITH NATIVE LIVER SUBGROUP
Change in ItchRO(Obs) severity score (SE)b
-2.16 (0.21)a
-1.01 (0.18)a
-1.15 0.0002
n=11 n=14
Percentage of days with pruritus improvement 96.4% 52.2% 44.1% 0.0045
n=11 n=14
Relative % change from baseline in total sBA -75.5% -9.0%
-73.1%c
<0.0001
n=11 n=14
a LS means (SE). LS mean, SE, and p-values are from MMRM model.
b ItchRO(Obs) = Itch Reported Outcome (Observer) is a Worst Itch 0-4 numerical rating scale.
c sBA treatment effects were estimated using log-transformed values and back-transformed to the original scale; therefore, they are not calculated as the arithmetic difference between treatment groups.
The primary endpoint represents change from baseline to the average of Weeks 13-20. Serum bile acid (sBA) endpoints represent change from baseline to the average of Weeks 12 and 20. Pruritus improvement was defined over Weeks 13-20 as a worst-daily ItchRO(Obs) score ≤1 or a decrease of ≥1 point from baseline. The All Pediatric Population included
randomized participants aged 18 years or younger who received at least one dose of study drug and had at least one ItchRO(Obs) score.
Safety Summary - 20-Week Double-Blind Period
The safety population includes all randomized participants who received at least one dose of maralixibat or placebo; participants were analyzed according to the treatment received.
Participants with, n (%) Maralixibat
285 µg/kg BID
(n=25) 		Placebo
(n=27)
Any treatment-emergent adverse event ("TEAE") 24 (96.0) 26 (96.3)
Grade 3 or higher TEAEs 6 (24.0) 6 (22.2)
Related to study drug 1 (4.0) 0
Serious TEAEs 5 (20.0) 5 (18.5)
TEAE that led to death 0 0
TEAE that led to premature discontinuation from study 1 (4.0) 0
TEAEs of interest
Diarrhea 16 (64.0) 3 (11.1)
Abdominal pain 5 (20.0) 4 (14.8)
ALT increased 2 (8.0) 1 (3.7)
Serious adverse events ("SAEs") in MRX-treated patients: pneumonia, pyrexia, large intestine infection, acute kidney injury, viral infection with bronchiolitis; none related. SAEs in placebo-treated patients: pneumonia, pancytopenia, sepsis, forearm fracture, cholangitis.
Patient Population Information
The Company believes the prevalent patient population in the United States and Europe for Livmarli for cholestatic pruritus in patients with Alagille syndrome ("ALGS") is approximately 4,000 - 5,500 pediatric ALGS patients, and of that prevalent population, approximately 2,000 pediatric ALGS patients are addressable, which, based on the Company's current expectations and beliefs, represents a greater than $500.0 million market opportunity. ALGS is estimated to impact one out of every 30,000 births globally.
The Company believes the addressable patient population in the United States and Europe for Livmarli for cholestatic pruritus in patients with progressive familial intrahepatic cholestasis ("PFIC") is approximately 1,000 pediatric PFIC patients and more than 4,000 adult PFIC patients.
The Company believes the addressable patient population in the United States and Europe for Livmarli for BA is approximately 2,000 BA patients.
The Company estimates that approximately 300 patients have been diagnosed in the United States with fibrodysplasia ossificans progressiva ("FOP") and that the prevalent patient population worldwide is approximately 900 FOP patients.
Mirum Pharmaceuticals Inc. published this content on October 13, 2026, and is solely responsible for the information contained herein. Distributed via EDGAR on October 13, 2026 at 12:12 UTC. If you believe the information included in the content is inaccurate or outdated and requires editing or removal, please contact us at [email protected]