December18, 2023
DyDo Pharma, Inc.

Submission of new drug application of amifampridine phosphate (3,4-diaminopyridine)for Lambert-Eaton myasthenic syndrome (LEMS) in Japan

DyDo Pharma, Inc., (Head Office: Kita-ku, Osaka; president and representative director: Yasunori Inaoka)

has submitted today a new drug application of a drug (DYD-301, generic name: amifampridinephosphate) for the treatment of Lambert-Eaton myasthenic syndrome (LEMS) to Pharmaceuticals andMedical Devices Agency (PMDA).
Amifampridine phosphate is a therapeutic agent for LEMS which DyDo Pharma has obtained from
Catalyst Pharmaceuticals, Inc. (Catalyst) for the co-exclusive development, manufacturing andmarketing license and the exclusive commercialization license for the treatment of LEMS in Japan, andthen DyDo Pharma has been developing for LEMS patients in Japan.
Amifampridine phosphate is an ethical product which has already been approved for use in thetreatment of LEMS in Europe, the U.S. and Canada. Catalyst has been marketing and sellingamifampridine tablets in the U.S. under the brand name of Firdapse®.

(Reference)
Lambert-Eaton myasthenic syndrome
Lambert-Eaton myasthenic syndrome is an autoimmune neuromuscular disorder in which a reduction inacetylcholine release from nerve terminals results in proximal muscle weakness, autonomic nervous
symptoms, and other symptoms. It is one of a number of paraneoplastic neurological syndromes that
accompany malignant tumors or precede tumors.

DYD-301 (amifampridine phosphate Tablets 10 mg)
DYD-301 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 theopening 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.
Amifampridine phosphate was granted orphan drug designation by the Ministry of Health, Labour andWelfare in Japan and has previously been approved for use for adults and for children ages six to seventeen
in the United States, and in Europe and Canada for the treatment of adults with LEMS.
Catalyst Pharmaceuticals
With exceptional patient focus, Catalyst is committed to developing and commercializing innovative firstin-class medicines that address rare neurological and epileptic diseases.

Catalyst's flagship U.S.

commercial product is FIRDAPSE® (amifampridine) Tablets 10 mg, approved for the treatment of LambertEaton myasthenic syndrome ("LEMS") for adults and children ages six to seventeen. In January 2023,
Catalyst acquired the U.S. commercial rights of FYCOMPA® (perampanel) CIII, a prescription medicine
approved in people with epilepsy aged four and older alone or with other medicines to treat partial-onset
seizures with or without secondarily generalized seizures, and with other medicines to treat primary
generalized tonic-clonic seizures for people with epilepsy aged 12 and older.

Further, Canada's national

healthcare regulatory agency, Health Canada, has approved the use of FIRDAPSE for the treatment of adultpatients in Canada with LEMS . On July 18, 2023, Catalyst acquired an exclusive license for North Americafor AGAMREE® (vamorolone) oral suspension 40 mg/mL, a novel corticosteroid treatment for Duchenne
Muscular Dystrophy. AGAMREE previously received FDA Orphan Drug and Fast Track designations andwas approved by the FDA for commercialization in the U.S. on October 26, 2023 with a launch planned forFirst Quarter 2024.
For

more

information

about

Catalyst

Pharmaceuticals,

Inc.,

visit

theCompany's

websiteat www.catalystpharma.com. For Full Prescribing and Safety Information for FIRDAPSE®, visit
www.firdapse.com. For Full Prescribing Information, including Boxed WARNING for FYCOMPA®, please
visit

www.fycompa.com.

ForFullPrescribing

InformationforAGAMREE,please

https://www.agamree.com/
Licensing Agreement between Catalyst and DyDo Pharma
Please see the press release issued on June 28, 2021 for more information about the agreement.
Notice of a Consolidated Subsidiary’s Entry into a Licensing Agreement

visit