Vamorolone Demonstrates On-Target Glucocorticoid Activity Without the Immunosuppression Characteristic of Traditional Corticosteroids at Clinical Doses (Form 8-K)

Vamorolone Demonstrates On-Target Glucocorticoid Activity Without the Immunosuppression Characteristic of Traditional Corticosteroids at Clinical Doses

Data Demonstrate Vamorolone's Balanced Corticosteroid Profile with On-Target Glucocorticoid Activity and Without Evidence of Significant Immunosuppressive Activity at Clinical Doses

CORAL GABLES, Fla., June 30, 2026 - Catalyst Pharmaceuticals, Inc. ("Catalyst") (Nasdaq: CPRX), a commercial-stage biopharmaceutical company focused on in-licensing, developing, and commercializing novel medicines for patients living with rare and difficult-to-treat diseases, today announced topline results from a two-part Phase 1 clinical study of vamorolone in healthy adult volunteers. The study demonstrated balanced corticosteroid activity with expected cortisol suppression and no evidence of significant immunosuppressive activity at clinical doses. These findings suggest that vamorolone delivers glucocorticoid and anti-inflammatory activity, while avoiding significant immunosuppressant effects, supporting its potential use as a treatment across a broad range of chronic inflammatory rare diseases.

Key Highlights and Readouts:

Overall study design

Part A: Vamorolone vs. deflazacort (equipotency assessment)

"By demonstrating similar cortisol suppression at label-based clinical doses of vamorolone and deflazacort, these data support the currently labeled dosing of vamorolone in the treatment of DMD and do not suggest the need for other dosing considerations when switching patients from deflazacort to vamorolone," said William Andrews, MD, Chief Medical Officer of Catalyst Pharmaceuticals. "Moreover, vamorolone achieved robust glucocorticoid and anti-inflammatory activity without evidence of significant immunosuppression at clinical doses."

Part B: Ascending dose evaluation of immunosuppressive potential

"As the 40 mg/kg/day dose is above currently approved vamorolone dosing and higher than doses previously studied in clinical trials, these findings suggest that clinically meaningful immunosuppression with vamorolone is unlikely at clinically relevant doses," Dr. Andrews added. "The prospect of this favorable profile-glucocorticoid and anti-inflammatory activity without clinically meaningful immunosuppression at clinically relevant doses-has the potential to distinguish vamorolone from conventional corticosteroids. Additionally, this profile may support vamorolone's potential utility across a broad range of chronically inflammatory rare diseases."

About Catalyst Pharmaceuticals, Inc.

Catalyst Pharmaceuticals, Inc. (Nasdaq: CPRX) is a biopharmaceutical company committed to improving the lives of patients with rare diseases. With a proven track record of bringing life-changing treatments to the market, we focus on in-licensing, commercializing, and developing innovative therapies. Guided by our deep commitment to patient care, we prioritize accessibility, ensuring patients receive the care they need through a comprehensive suite of support services designed to provide seamless access and ongoing assistance. Catalyst maintains a well-established U.S. presence, which remains the cornerstone of our commercial strategy, while continuously evaluating strategic opportunities to expand our global footprint. Catalyst, headquartered in Coral Gables, Fla., has been recognized by Forbes as one of America's Most Successful Companies in 2023, 2024, and 2025, and on the 2025 Deloitte Technology Fast 500^™ list as one of North America's Fastest-Growing Companies.

For more information, please visit Catalyst's website at www.catalystpharma.com.