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# FDA Orphan Status for Catalyst Firdapse in New Indication
- URL: https://www.fdaweb.com/fda-orphan-status-for-catalyst-firdapse-in-new-indication/
- Published: 2016-09-02T12:00:00.000Z
- Updated: 2026-09-14T21:29:21.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5136690

FDA has granted Catalyst Pharmaceuticals an orphan drug designation for Firdapse (amifampridine phosphate) for treating myasthenia gravis. The rare disease is caused by antibodies to the muscle-specific kinase (MuSK-MG) and is “characterized by a predominance in females, prominent bulbar involvement, more severe clinical condition and resistance to treatment,” the company says. Although many patients with MuSK-MG are presently treated with anticholinesterase inhibitors or immunosuppressants, such patients do not generally respond adequately to these treatments.

Earlier this year, FDA issued a refuse-to-file letter and told Catalyst that it will need positive results from an additional study to support an NDA submission for a separate indication — symptomatic treatment of Lambert-Eaton myasthenic syndrome (LEMS). The agency also said it wanted several additional short-term toxicology studies, according to the company. The drug has been given breakthrough therapy and orphan drug designations for its proposed LEMS indication.

In June, FDA and Catalyst reached agreement on a confirmatory Phase 3 study protocol for Firdapse use in LEMS. As part of the clinical protocol for the confirmatory study, Catalyst says it will initiate a small, single-center study with Firdapse during the second half of 2016\. The company says it will announce additional information about the study design and timelines for the study once they are finalized.