First Patient Enrolled in Phase 3 Trial of Firdapse in MuSK Antibody Positive Myasthenia Gravis


The first patient was enrolled in a Phase 3 clinical trial of amifampridine phosphate (Firdapse) in patients with mmuscle-specific kinase (MuSK) antibody positive myasthenia gravis (MuSK-MG).

This morning, Catalyst Pharmaceuticals, Inc announced the enrollment of its first patient in its Phase 3 clinical trial of amifampridine phosphate (Firdapse) in patients with muscle-specific kinase (MuSK) antibody positive myasthenia gravis (MuSK-MG).

Myasthenia gravis (MG) is a rare autoimmune disease that affects the neuromuscular junction, which is the site where nerve cells and muscle cells communicate, while MuSK is a second chemical necessary for proper nerve-muscle communication. MuSK-MG is when the patients’ bodies attack cells that produce the MuSK chemical needed to conduct nerve-muscle communication across the neuromuscular junction. Approximately 8% of all people with MG in the US suffer from the MuSK-MG type (about 3,000-4,800 total patients).

Gary Ingenito, MD, PhD, Chief Medical Officer of Catalyst, highlighted the significance of the Phase 3 trial and its first enrolled participant. “There is a significant, unmet medical need to treat the symptoms of MuSK-MG, and these patients are eagerly awaiting a new treatment option. The previous Catalyst supported, proof-of-concept investigator-sponsored study in MuSK-MG patients showed impressive clinical improvement in multiple measures. We’re pleased to have begun enrolling patients in this study and look forward to working closely with the MG community to advance Firdapse through this Phase 3 trial.”1

The MSK-002 Phase 3 clinical trial of Firdapse is a double-blind, placebo-controlled withdrawal trial that will be conducted in both the US and Italy. The trial will aim to enroll 60 adult participants diagnosed with MuSK-MG. Per the FDA’s request, additional generalized myasthenia gravis patients (up to 10) will be enrolled. This subgroup of the participant population will be assessed with the same clinical endpoints; however, they are not required to achieve statistical significance, and only summary statistics will be provided.

The primary endpoint of the study is to assess and measure the safety and efficacy of amifampridine phosphate in improving the activities of daily living for patients with antibody positive MuSK-MG. Two study arms will be included: the experimental and placebo comparator. Participants in the experimental arm will be administered tablets equivalent to 10mg amifampridine, titrated to an efficacious and tolerable dose 3 to 4 times a day. Participants in the placebo comparator will be administered tablets matching amifampridine phosphate 3 to 4 times a day.2

The Myasthenia Gravis Activities of Daily Living (MG-ADL), which asses the rapid symptom severity, will be the primary outcome measure. The Quantitative Myasthenia Gravis Score (QMG), which is a standardized quantitative strength scoring system of the disease severity, will be the secondary outcome measure. The trial is anticipated to take 12 months to complete.

Patrick J. McEnany, Chairman and CEO of Catalyst, reiterated the importance of the trial. “By conducting this Phase 3 study in patients with MuSK-MG, we hope to provide a potential treatment option for people suffering from this rare condition. Catalyst continues to build a leadership position in developing therapies to treat rare neuromuscular diseases with this next step for an important investigational product to potentially treat the symptoms of MuSK-MG.”

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  1. Catalyst Pharmaceuticals Announces Enrollment of First Patient in Phase 3 Trial of Firdapse® in MuSK Antibody Positive Myasthenia Gravis. Accessed April 19, 2018.
  2. Study to Evaluate Amifampridine Phosphate in Patients With MuSK-MG.” Accessed April 19, 2018.
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