What happened
On October 12, Mirum reported phase 3 EXPAND results for maralixibat, already sold as Livmarli for other indications. The study tested whether it could relieve cholestatic pruritus, itching associated with impaired bile flow, in people aged at least six months with additional ultra-rare liver diseases, including biliary atresia. During the 20-week blinded comparison, 52 participants received maralixibat or placebo. The proposed additional U.S. use has not been approved.
Why it matters
For people living with cholestatic disease, itching is a symptom that matters in its own right. EXPAND reports improvement on the observer-rated itch measure alongside a fall in serum bile acids, providing two distinct kinds of evidence for the proposed use. The much higher reported diarrhea rate is part of the same practical picture: a symptom benefit must be considered with tolerability, and neither the trial result nor an existing approval for other indications makes this additional use approved.
Evidence
The primary itch analysis included 46 children. On an observer-rated worst-itch scale from 0 to 4, the average improvement over weeks 13–20 was 1.81 points in 22 children given maralixibat and 0.83 points in 24 given placebo. The between-group treatment difference was 0.98 points (p=0.0004). Children met the study’s definition of itch improvement on 86.0% of days with treatment, compared with 49.1% with placebo. These results describe a difference in an observed symptom, not just a change in a blood test.
Across all 52 participants, serum bile acids fell 70.1% from baseline with maralixibat versus 3.5% with placebo. The filing reports a model-derived 69.0% treatment effect; it is not the simple subtraction of those two percentages. In the 25-person biliary-atresia subgroup retaining their native liver, the itch-score difference was 1.15 points versus placebo. Subgroup results are informative but come from fewer people than the overall trial.
Diarrhea occurred in 16 of 25 maralixibat recipients (64.0%) and 3 of 27 placebo recipients (11.1%). Serious treatment-emergent events occurred in five participants in each arm, and the sponsor reported no new safety signal. The results come from a sponsor filing with the SEC, not an FDA determination for the proposed use. (sec.gov)
What remains unknown
EXPAND is small, especially when divided among individual diseases, and its reported blinded comparison lasted 20 weeks. It therefore cannot yet establish how durable the itch relief will be or how tolerability will look over longer treatment. The eventual scope of any U.S. label expansion also depends on an application and regulatory review.
Who may be affected
People with the rare cholestatic liver diseases studied in EXPAND, particularly children with severe itching, and the clinicians and researchers assessing a possible future treatment option.
AXIONOVA connection
EXPAND measured both a symptom patients experience and a related laboratory marker, serum bile acids. The planned supplemental U.S. application and review of efficacy and tolerability across disease subgroups are the next steps to watch; this readout alone does not establish a new indication.
What ALETHA can explain
ALETHA can explain why the 0.98-point result is the difference between groups rather than either group’s improvement from baseline, and why itch scores and serum bile acids answer related but different questions.
Action posture
Monitor: The result is consequential, but this additional U.S. use awaits an application and regulatory review.