Mirum Pharmaceuticals had a good Monday morning. The company (NASDAQ:MIRM) reported topline results from its Phase 3 EXPAND study, which tested LIVMARLI (maralixibat) in people aged six months and older dealing with cholestatic pruritus tied to ultra-rare cholestatic liver conditions, biliary atresia among them. The stock traded higher after the announcement.

The trial didn't just clear its primary endpoint. It hit statistical significance across all five prespecified secondary measures, including three key outcomes in biliary atresia patients who still had their native liver. That's the kind of clean sweep that makes a biotech morning pleasant.

What The Phase 3 EXPAND Trial Actually Showed

The late-stage study enrolled 52 participants who received either maralixibat at 285 µg/kg twice daily or a placebo. In the main pediatric analysis population, maralixibat generated a statistically significant reduction in itching compared to placebo.

Between Weeks 13 and 20, patients on maralixibat saw a 1.81-point mean improvement from baseline in their average worst-daily ItchRO(Obs) severity score. The placebo group managed 0.83 points. That works out to a placebo-adjusted treatment difference of 0.98 points (p=0.0004).

The bile acid numbers were even more lopsided. Maralixibat drove a 70.1% drop from baseline in total serum bile acids, versus 3.5% for placebo, for a 69.0% treatment effect. Pediatric patients on the drug also achieved pruritus improvement on 86.0% of days, compared to 49.1% for placebo.

The Biliary Atresia Subgroup Looked Even Better

Among patients with biliary atresia who retained their native liver, the clinical improvements were substantial. Those taking maralixibat achieved a 2.16-point reduction in severity score versus a 1.01-point drop for placebo, a 1.15-point difference.

These patients experienced pruritus relief on 96.4% of days compared to 52.2% for placebo (p=0.0045). Maralixibat also achieved a 75.5% reduction in total serum bile acids compared to 9.0% for placebo.

Safety Stayed Boring, Which Is The Goal

Safety outcomes mirrored previous clinical trials, and researchers identified no new safety concerns.

Serious adverse events in the maralixibat cohort included pneumonia, pyrexia, large intestine infection, acute kidney injury, and viral infection with bronchiolitis, though none were deemed treatment-related. The placebo group's serious adverse events included pneumonia, pancytopenia, sepsis, forearm fracture, and cholangitis.

MIRM Price Action: Mirum Pharmaceuticals shares were up 2.31% at $88.00 during premarket trading on Monday, according to market data.