Mirum posts positive volixibat Phase 2b PSC results

Mirum Pharmaceuticals reported that its VISTAS Phase 2b study of volixibat in primary sclerosing cholangitis met the primary endpoint for cholestatic itch relief.

Rhea-AI Filing Summary

Mirum Pharmaceuticals reported that its VISTAS Phase 2b study of volixibat in primary sclerosing cholangitis met the primary endpoint for cholestatic itch relief. In the primary analysis cohort, volixibat 20 mg twice daily achieved a 2.72-point improvement on the Adult ItchRO scale versus 1.08 points for placebo, for a placebo-adjusted difference of 1.64 points (p<0.0001).

Statistically significant itch reductions appeared within two weeks and were also seen in patients with mild baseline itch. Safety was consistent with ileal bile acid transporter inhibition, with more gastrointestinal events and liver test elevations; diarrhea occurred in 40.3% of volixibat patients versus 8.6% on placebo, and more patients on volixibat discontinued treatment due to adverse events.

The company has a pre-New Drug Application meeting with the U.S. FDA for volixibat in PSC planned for summer 2026 and is targeting an NDA submission in the second half of 2026. Mirum also expects topline data from the VANTAGE Phase 2b volixibat study in primary biliary cholangitis in the first quarter of 2027.

Positive

• Phase 2b primary endpoint met with strong statistics: Volixibat reduced Adult ItchRO scores by 2.72 points versus 1.08 for placebo, for a placebo-adjusted difference of 1.64 points (p<0.0001), supporting its potential as the first treatment for cholestatic pruritus in PSC.
• Clear regulatory path outlined: The company has a pre-NDA meeting with the FDA scheduled for summer 2026 and is planning a New Drug Application submission for volixibat in PSC in the second half of 2026.

Negative

• High rate of gastrointestinal side effects and discontinuations: Diarrhea occurred in 40.3% of volixibat-treated patients versus 8.6% on placebo, with more treatment-emergent adverse events and higher premature discontinuation rates, which may affect long-term tolerability and adoption.

Insights

Biotech and drug development analyst

Strong itch efficacy in PSC de-risks volixibat and supports an NDA path, with notable but expected GI side effects.

The VISTAS Phase 2b data show volixibat delivering a 2.72-point itch reduction versus 1.08 with placebo, yielding a 1.64-point placebo-adjusted benefit on Adult ItchRO (p<0.0001). Achieving the prespecified primary endpoint in PSC pruritus is important because there are currently no approved treatments specifically for this symptom.

Benefits emerged within two weeks and extended to patients with mild baseline itch, suggesting broad symptomatic impact. The safety profile aligns with known IBAT inhibitor effects: high overall treatment-emergent adverse events and substantially higher diarrhea (40.3% vs 8.6% with placebo), plus more discontinuations and some liver lab elevations, which may influence labeling and real-world tolerability.

Mirum is planning a pre-NDA FDA meeting in summer 2026 and targeting an NDA submission in the second half of 2026, positioning volixibat as a potential first treatment for cholestatic pruritus in PSC. Additional risk and opportunity come from the upcoming VANTAGE Phase 2b readout in primary biliary cholangitis expected in Q1 2027, which will further define volixibat’s broader cholestatic disease profile.

8-K Event Classification

Item 8.01 — Other Events

1 item

Item 8.01 Other Events Other

Voluntary disclosure of events the company deems important to shareholders but not covered by other items.

Key Figures

Primary analysis cohort size: 111 patients Total VISTAS enrollment: 158 patients Itch reduction with volixibat: 2.72 points +5 more

8 metrics

Primary analysis cohort size 111 patients PSC patients with moderate to severe itch in VISTAS Phase 2b

Total VISTAS enrollment 158 patients All PSC patients across primary and secondary cohorts

Itch reduction with volixibat 2.72 points LS mean change in Adult ItchRO in primary cohort

Itch reduction with placebo 1.08 points LS mean change in Adult ItchRO in primary cohort

Placebo-adjusted itch benefit 1.64 points Difference in Adult ItchRO change (volixibat minus placebo)

Diarrhea incidence volixibat 40.3% Patients on volixibat with diarrhea TEAE (77 treated)

Diarrhea incidence placebo 8.6% Patients on placebo with diarrhea TEAE (81 treated)

Pre-NDA meeting timing Summer 2026 Planned FDA meeting for volixibat in PSC

Key Terms

primary sclerosing cholangitis, cholestatic pruritus, Adult Itch Reported Outcome, treatment emergent adverse event, +2 more

6 terms

primary sclerosing cholangitis medical

"volixibat, an investigational oral ileal bile acid transporter inhibitor, in patients with primary sclerosing cholangitis"

A chronic disease in which the tubes that carry bile from the liver become inflamed and scarred, gradually blocking flow and potentially causing liver damage or failure; think of it like corrosion and narrowing in the body’s plumbing that disrupts normal cleanup and digestion. It matters to investors because there is no widely effective cure, so diagnostic advances, drugs, or procedures that slow progression can create meaningful commercial markets and clinical trial, regulatory and pricing risks that affect valuations in healthcare and biotech companies.

cholestatic pruritus medical

"support the potential for volixibat to become the first treatment for cholestatic pruritus in patients with PSC"

Severe itching caused by impaired bile flow from the liver into the gut, where substances that normally leave the body build up and irritate nerve endings in the skin. Investors should care because this symptom can drive demand for treatments, shape clinical trial measures and regulatory decisions, and affect a drug’s safety profile and market potential—much like a visible fault that influences customer trust and product value.

Adult Itch Reported Outcome medical

"as measured by the Adult Itch Reported Outcome scale"

treatment emergent adverse event medical

"Participants with any treatment emergent adverse event, n (%)"

A treatment-emergent adverse event is any new or worsening unwanted medical effect that appears after a patient starts a drug or medical intervention during a clinical trial. Think of it like side effects that show up only after someone begins a new medicine; these events matter to investors because they shape a therapy’s safety record, influence regulators’ approval decisions, affect trial continuation, and can materially change a product’s commercial prospects and company valuation.

Phase 2b study medical

"The VISTAS Phase 2b study included 158 patients with PSC"

A phase 2b study is a mid-stage clinical trial that focuses on finding the right dose and confirming whether a drug has the intended effect in a larger group of patients than early tests. Think of it as an extended test drive to fine-tune settings and prove the product works before the big, final trials; for investors, positive phase 2b results materially reduce technical risk and often change a company’s development value and financing prospects.

New Drug Application regulatory

"The Company has a pre-New Drug Application meeting for volixibat in PSC scheduled"

A new drug application is a formal request submitted to government regulators seeking approval to market a new medicine. It is like a detailed proposal that shows the drug has been tested for safety and effectiveness. For investors, receiving approval signals that the drug may soon become available for sale, potentially leading to revenue growth and impacting the company's value.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

What did Mirum Pharmaceuticals (MIRM) report from the VISTAS Phase 2b PSC trial?

Mirum reported that its VISTAS Phase 2b study of volixibat in primary sclerosing cholangitis met the primary pruritus endpoint. Volixibat showed a 2.72-point itch reduction versus 1.08 points for placebo, yielding a placebo-adjusted benefit of 1.64 points with p<0.0001.

How effective was volixibat at reducing itch in Mirum’s PSC study?

Volixibat 20 mg twice daily reduced Adult ItchRO scores by 2.72 points in the primary cohort, compared with 1.08 points for placebo. This produced a placebo-adjusted improvement of 1.64 points in the primary endpoint, with highly statistically significant results (p<0.0001).

What safety profile did volixibat show in Mirum’s VISTAS Phase 2b trial?

Safety was generally consistent with IBAT inhibition, with more gastrointestinal and liver-related effects. Diarrhea occurred in 40.3% of volixibat patients versus 8.6% on placebo, and more volixibat-treated patients discontinued early due to treatment-emergent adverse events, including diarrhea.

What are Mirum Pharmaceuticals’ regulatory plans for volixibat in PSC?

Mirum plans a pre-New Drug Application meeting with the U.S. FDA in summer 2026 to discuss volixibat in PSC. The company then aims to submit an NDA in the second half of 2026, potentially positioning volixibat as a first treatment for cholestatic pruritus in PSC.

When will Mirum (MIRM) share more clinical data on volixibat?

Mirum will present full VISTAS Phase 2b results in a late-breaking oral session at the European Association for the Study of the Liver International Liver Congress on May 30, 2026. The company also expects topline VANTAGE Phase 2b data in primary biliary cholangitis in the first quarter of 2027.

How many patients were enrolled in Mirum’s VISTAS Phase 2b PSC study?

The VISTAS Phase 2b trial enrolled 158 patients with primary sclerosing cholangitis. Of these, 111 formed the primary analysis cohort with moderate to severe itch, and 47 formed a secondary cohort with mild itch. Patients received volixibat 20 mg twice daily or placebo.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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Accepted by SEC EDGAR 05/04/2026 - 08:00 AM Learn about SEC filing dates

false 0001759425 0001759425 2026-05-04 2026-05-04

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 8-K

CURRENT REPORT

Pursuant to Section 13 or 15(d)

of the Securities Exchange Act of 1934

Date of Report (Date of earliest event reported): May 4, 2026

Mirum Pharmaceuticals, Inc.

(Exact name of registrant as specified in its charter)

Delaware		001-38981		83-1281555
(State or other jurisdiction of incorporation)		(Commission File Number)		(IRS Employer Identification No.)
989 East Hillsdale Boulevard
Suite 300
Foster City, California				94404
(Address of principal executive offices)				(Zip Code)

Registrant’s telephone number, including area code: (650) 667-4085

N/A

(Former name or former address, if changed since last report)

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions:

☐ Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

☐ Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

☐ Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

☐ Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

Securities registered pursuant to Section 12(b) of the Act:

Title of each class		Trading Symbol(s)		Name of each exchange on which registered
Common stock, par value $0.0001 per share		MIRM		Nasdaq Global Market

Indicate by check mark whether the registrant is an emerging growth company as defined in Rule 405 of the Securities Act of 1933 (§ 230.405 of this chapter) or Rule 12b-2 of the Securities Exchange Act of 1934 (§ 240.12b-2 of this chapter).

Emerging growth company ☐

If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 13(a) of the Exchange Act. ☐

Item 8.01 Other Events.

On May 4, 2026, Mirum Pharmaceuticals, Inc. (the “Company”) announced the primary endpoint was met in the VISTAS Phase 2b study evaluating volixibat, an investigational oral ileal bile acid transporter (“IBAT”) inhibitor, in patients with primary sclerosing cholangitis (“PSC”).

The VISTAS Phase 2b study included 158 patients with PSC who were assigned to either a primary analysis cohort (moderate to severe itch; n=111) or a secondary analysis cohort (mild itch; n=47) based on itch severity at baseline, as measured by the Adult Itch Reported Outcome (“ItchRO”) scale. Patients in both cohorts were treated with volixibat 20 mg twice daily (“BID”) or placebo. Per the study protocol, the endpoint was evaluated in the primary analysis cohort.

The results of the VISTAS Phase 2b study support the potential for volixibat to become the first treatment for cholestatic pruritus in patients with PSC. In the primary analysis cohort, treatment with volixibat demonstrated a robust 2.72 point improvement in pruritus and a placebo-adjusted difference of 1.64 points in the primary endpoint (p<0.0001), as measured by the Adult ItchRO scale, reflecting change from baseline to the average of the last 12 weeks of treatment. Statistically significant improvements in pruritus were observed within two weeks of treatment and were also observed in the secondary cohort of patients with mild itch at baseline. Key efficacy data from the VISTAS Phase 2b study are presented below in the Change from Baseline (Primary Analysis Cohort) table.

Volixibat’s safety profile was generally consistent with the known effects of IBAT inhibition, characterized primarily by gastrointestinal adverse events and elevations in liver laboratory parameters, including alanine aminotransferase (“ALT”) and bilirubin. Key safety data from the VISTAS Phase 2b study are presented below in the Safety Summary (Primary and Secondary Cohorts) table.

The Company has a pre-New Drug Application (“NDA”) meeting for volixibat in PSC scheduled with the U.S. Food and Drug Administration (“FDA”) in summer 2026, with a planned NDA submission in the second half of 2026.

The full results from the VISTAS Phase 2b study will be presented in a late-breaking oral presentation at the European Association for the Study of the Liver International Liver Congress on May 30 at 2:15 p.m. CEST.

The Company also now expects topline data from its VANTAGE Phase 2b study of volixibat in primary biliary cholangitis (“PBC”) in the first quarter of 2027.

Change from Baseline (Primary Analysis Cohort)

		Volixibat 20 mg BID (n=54)		Placebo (n=57)		Difference (VLX - PBO)		p-value
LS Mean change in Adult ItchRO (SE)*		-2.72 (0.240)		-1.08 (0.241)		-1.64		<0.0001
≥2 point reduction in Adult ItchRO*		55.6%		26.3%		29.3%		0.0019
LS Mean changes in sBA (SE)		-33.7 (12.14)		2.1 (11.87)		-35.8		0.0324

* Adult ItchRO is an 11-point scale (0 = no itch; 10 = worst itch imaginable). LSMean = model-adjusted mean from a mixed model for repeated measures (MMRM). Values represent change from baseline to the average of the last 12 weeks of treatment (weekly averaged worst daily itch score).

2

Safety Summary (Primary and Secondary Cohorts)

		Volixibat 20 mg BID (n=77)		Placebo (n=81)
Participants with any treatment emergent adverse event (“TEAE”), n (%)		72 (93.5)		68 (84.0)
Grade 3 or higher TEAEs		10 (13.0)		9 (11.1)
Serious TEAEs		8 (10.4)		5 (6.2)
TEAE that led to death		0		1 (1.2)
TEAE that led to premature discontinuation from study		7 (9.1)		2 (2.5)
Study discontinuation due to diarrhea		3 (3.9)		1 (1.2)

Additional safety observations:

• Serious adverse events (“SAEs”) in volixibat treated patients included cholangitis, infection (sepsis, liver abscess, viral infection), abdominal pain, cholangiocarcinoma, sclerosing cholangitis, biliary colic, pyrexia, back pain, procedure-related pancreatitis; none related. SAEs in placebo patients included cholangitis, constipation, spontaneous bacterial peritonitis, liver function tests increases, radius fracture.

• Elevations in ALT, Aspartate Aminotransferase (“AST”), Alkaline Phosphatase (“ALP”), and bilirubin were observed more frequently in volixibat treated patients than placebo treated patients.

TEAEs Occurring in ≥5% of Patients (Primary and Secondary Cohorts)

n (%)		VLX 20 mg (N=77)		Placebo (N=81)
Diarrhea		31 (40.3)		7 (8.6)
Abdominal Pain		14 (18.2)		8 (9.9)
Nausea		10 (13.0)		3 (3.7)
Vitamin D deficiency		8 (10.4)		4 (4.9)
Abdominal pain upper		7 (9.1)		6 (7.4)
ALT increased		7 (9.1)		3 (3.7)
Upper respiratory tract infection		6 (7.8)		6 (7.4)
Back pain		5 (6.5)		2 (2.5)
Fatigue		5 (6.5)		4 (4.9)
Blood bilirubin increased		4 (5.2)		3 (3.7)
Jaundice		4 (5.2)		1 (1.2)
Pyrexia		4 (5.2)		1 (1.2)
Influenza		3 (3.9)		5 (6.2)

Forward-Looking Statements

Certain statements contained in this report are forward-looking statements that involve a number of risks and uncertainties. Such forward-looking statements include, without limitation, statements regarding the expected occurrence and timing of potential meetings with the FDA and NDA submission, the potential benefits of volixibat, the use of cholestatic pruritus as an important endpoint in PSC and the success or approval of any potential regulatory submission for volixibat. The inclusion of forward-looking statements should not be regarded as a representation by the Company that any of these results will be achieved. Actual results may differ from those set forth in this report due to the risks and uncertainties associated with research and development of pharmaceutical product candidates, as well as risks and uncertainties inherent in the Company’s business, including those described in the Company’s other filings with the U.S. Securities and Exchange Commission. You are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date hereof, and the Company undertakes no obligation to revise or update any forward-looking statements to reflect events or circumstances after the date hereof. All forward-looking statements are qualified in their entirety by this cautionary statement. This caution is made under the safe harbor provisions of Section 21E of the Private Securities Litigation Reform Act of 1995.

3

SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the registrant has duly caused this report to be signed on its behalf by the undersigned thereunto duly authorized.

				Mirum Pharmaceuticals, Inc.
Date: May 4, 2026				By:		/s/ Christopher Peetz
						Christopher Peetz
						Chief Executive Officer

4

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