Catalyst Pharma’s Firdapse Fails in Late Stage Trial in Myasthenia Gravis

Catalyst Pharmaceuticals’ Firdapse did not meet its primary and secondary endpoints in phase 3 trial evaluating it as a treatment for patients with MuSK myasthenia gravis.

The news was contained in a release reporting the company’s second quarter results and does not bode well for Catalyst’s attempt to expand its approved use beyond Lambert-Eaton myasthenic syndrome (LEMS), a rare neuromuscular disorder that makes it difficult to move the muscles normally.

Myasthenia gravis (MG) is a rare autoimmune neuromuscular disease that affects skeletal muscles responsible for eye movements, breathing, and body motion, causing muscle weakness and fatigue. It is caused by the failure of neuromuscular transmission, which results from the binding of autoantibodies to proteins involved in signaling.

MuSK-MG is a subclass of the disease that occurs mostly in females, has an earlier onset than other MG subclasses, prominent bulbar involvement affecting motor neurons involved in speech and swallowing, a more severe clinical condition, and significant resistance to treatment. It is estimated to affect up to 8 percent of all patients with MG and its presentation can range from mild to severe.

Although many patients with MuSK-MG are treated with anticholinesterase inhibitors or immunosuppressants, they do not respond well to such treatments.

Catalyst’s MuSK trial is a phase 3, randomized, double blind, placebo-controlled, parallel-group study evaluating the safety, tolerability, and efficacy of Firdapse in patients with MuSK-MG and a small sample of patients with AChR-MG.

Catalyst reported that Firdapse was safe and well tolerated and demonstrated a safety profile similar to that seen for Firdapse in the treatment of LEMS. However, neither the primary endpoint, the Myasthenia Gravis Activities of Daily Living assessment, nor the secondary endpoint, the Quantitative Myasthenia Gravis assessment, achieved statistical significance.

Catalyst said it plans to complete the full analysis of data and findings and to meet with its neuromuscular advisors to decide a path forward for the MuSK-MG indication.

Detailed results of the study will be made available in a future scientific forum.

Catalyst has been mired in controversy over pricing since it gained U.S. Food and Drug Administration approval of Firdapse in late 2018 to treat patients with LEMS. It’s active ingredient amifampridine, a neuronal potassium channel blocker, had been available for free for many years under a compassionate use program before Firdapse was approved and Catalyst quickly announced a list price of $375,000 when it was launched in January 2019. The company held firm to the price but said it developed several financial assistance programs, that it said would reduce “in most cases the patient’s monthly out-of-pocket expense will be $10 or less.”