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Catalyst Pharmaceuticals Announces Publication of Clinical Data from the Investigator-Sponsored Phase IIb Study Evaluating Firdapse® for the Treatment of MuSK Antibody Positive Myasthenia Gravis

Published online in SAGE Open Medicine on December 17, 2018

CORAL GABLES, Fla., Jan. 04, 2019 (GLOBE NEWSWIRE) -- Catalyst Pharmaceuticals, Inc. (Catalyst) (Nasdaq: CPRX), a biopharmaceutical company focused on developing and commercializing innovative therapies for people with rare debilitating, chronic neuromuscular and neurological diseases, today announced the online publication in SAGE Open Medicine of the results of an investigator-sponsored Phase IIb clinical trial (MSK-001) evaluating Firdapse® (amifampridine phosphate) for the treatment of MuSK antibody positive Myasthenia Gravis (MuSK-MG).

The positive topline results from this trial were previously announced, but the full results of safety, efficacy and other clinical data are now available online. The MSK-001 trial was a randomized, double-blind, placebo-controlled, double crossover design. The co-primary endpoints were statistically met (QMG score: p=0.0003 and MG-Activities of Daily Living Profile Score: p=0.0006) as well as the secondary endpoints. The study provided evidence that amifampridine phosphate was safe and effective in treating MuSK-MG patients. The study was conducted under the supervision of Silvia Bonanno, M.D. and her team at the Istituto Neurologico Carlo Besta in Milan, Italy.

These data are more fully described in the manuscript entitled, “Amifampridine phosphate in the treatment of muscle-specific kinase myasthenia gravis: a phase IIb, randomized, double-blind, placebo-controlled, double crossover study”, which was recently published online in SAGE Open Medicine. The article can be accessed at: .

“The results of the pilot study are very encouraging, such that our multi-center pivotal Phase 3 trial evaluating Firdapse for the treatment of MuSK-MG is currently underway. Our pivotal trial is being conducted under an FDA Special Protocol Assessment (SPA),” said Gary Ingenito, M.D., Ph.D., Chief Medical Officer of Catalyst Pharmaceuticals. “If our Phase 3 trial is successful, we hope that Catalyst will be able to offer physicians and patients alternatives in the treatment of MuSK-MG.”

About MuSK antibody positive Myasthenia Gravis (MG)

About 15% of MG patients test negative for the acetylcholine receptor antibody. These patients have seronegative (SN) MG. Approximately 40-50% of these patients with SNMG (equating to an estimate of approximately 4,500 patients in the United States) test positive for the anti-MuSK antibody. MuSK is a protein that is required for the maintenance of the neuromuscular junction and patients with the anti-MuSK antibody are identified as having MuSK-MG. MuSK-MG is a clinically distinguishable, more severe form of MG. The disease is characterized by a predominance in females, a prevalent involvement of cranial and bulbar muscles, high incidence of respiratory crises and a resistance to treatment. Although many patients with MuSK-MG are presently treated with anticholinesterase inhibitors or immunosuppressants, such patients do not generally respond adequately to these treatments.

About Catalyst Pharmaceuticals

Catalyst Pharmaceuticals is a biopharmaceutical company focused on developing and commercializing innovative therapies for people with rare debilitating, chronic neuromuscular and neurological diseases, including LEMS, congenital myasthenic syndromes (CMS), MuSK antibody positive myasthenia gravis (MuSK-MG), and spinal muscular atrophy (SMA) type 3. Catalyst's new drug application for Firdapse® (amifampridine) 10 mg tablets for the treatment of adults with Lambert-Eaton Myasthenic Syndrome (LEMS) was recently approved by the U.S. Food & Drug Administration ("FDA"), and Firdapse is expected to be commercially available in the United States early in the first quarter of 2019. Prior to its approval, Firdapse for LEMS had received breakthrough therapy designation and orphan drug designation from the FDA.

Firdapse is currently being evaluated in clinical trials for the treatment of CMS, MuSK-MG and SMA type 3 and has received Orphan Drug Designation from the FDA for CMS and myasthenia gravis. Firdapse (amifampridine) 10 mg tablets is the first and only approved drug in Europe for the symptomatic treatment in adults with LEMS.

About Firdapse® (amifampridine)

Firdapse® (amifampridine) 10 mg tablets is an oral, nonspecific, voltage-dependent, potassium (K+) channel blocker that causes depolarization of the presynaptic membrane and slows or inhibits repolarization. This action results in the opening of slow voltage-dependent calcium (Ca2+) channels, allowing for a subsequent influx of Ca2+. In turn, it induces the exocytosis of synaptic vesicles containing Acetylcholine (ACh) to release more ACh into the synaptic cleft, enhancing neuromuscular transmission, and providing for improved muscle function. Firdapse is approved in the U.S. and the European Union for use by patients with LEMS.

Important Safety Information


FIRDAPSE is contraindicated in patients with:

  • A history of seizures
  • Hypersensitivity to amifampridine phosphate or another aminopyridine


Seizures: FIRDAPSE can cause seizures. Consider discontinuation or dose reduction of FIRDAPSE in patients who have a seizure while on treatment. FIRDAPSE is contraindicated in patients with a history of seizures.

Hypersensitivity: If a hypersensitivity reaction such as anaphylaxis occurs, FIRDAPSE should be discontinued and appropriate therapy initiated.


The most common (> 10%) adverse reactions are: paresthesia, upper respiratory tract infection, abdominal pain, nausea, diarrhea, headache, elevated liver enzymes, back pain, hypertension, and muscle spasms.

To report SUSPECTED ADVERSE REACTIONS, contact Catalyst Pharmaceuticals at 1-844-347-3277 (1‑844-FIRDAPSE) or FDA at 1-800-FDA-1088 or

Forward-Looking Statements

This press release contains forward-looking statements. Forward-looking statements involve known and unknown risks and uncertainties, which may cause Catalyst's actual results in future periods to differ materially from forecasted results. A number of factors, including (i) whether Catalyst will be successful in commercializing Firdapse (ii) whether, even if Catalyst is successful in commercializing Firdapse, Catalyst will become profitable, (iii) whether Catalyst’s ongoing clinical trials evaluating Firdapse for the treatment of CMS, MuSK-MG and SMA type 3 will be successful; (iv) whether Firdapse will ever be approved for the treatment of CMS, MuSK-MG, SMA type 3, or any other disease, and (v) those other factors described in Catalyst's Annual Report on Form 10-K for the fiscal year 2017 and its other filings with the U.S. Securities and Exchange Commission (SEC), could adversely affect Catalyst. Copies of Catalyst's filings with the SEC are available from the SEC, may be found on Catalyst's website, or may be obtained upon request from Catalyst. Catalyst does not undertake any obligation to update the information contained herein, which speaks only as of this date.

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