Amifampridine

Amifampridine phosphate is used as a drug, predominantly in the treatment of a number of rare muscle diseases. The free base form of the drug has been used to treat congenital myasthenic syndromes and approved by the FDA for Lambert–Eaton myasthenic syndrome (LEMS) through compassionate use programs since the 1990s and was recommended as a first line treatment for LEMS in 2006, using ad hoc forms of the drug, since there was no marketed form.

Around 2000 doctors at Assistance Publique – Hôpitaux de Paris created a phosphate salt form, which was developed through a series of companies ending with BioMarin Pharmaceutical which obtained European approval in 2009 under the brand name Firdapse, and which licensed the US rights to Catalyst Pharmaceuticals in 2012. As of January 2017, Catalyst and another US company, Jacobus Pharmaceutical, which had been manufacturing and giving it away for free since the 1990s, were both seeking FDA approval for their iterations and marketing rights.

Amifampridine phosphate (Firdapse) has orphan drug status in the EU for Lambert–Eaton myasthenic syndrome and Catalyst holds both an orphan designation and a breakthrough therapy designation in the US. In May 2019, the US Food and Drug Administration (FDA) approved amifampridine tablets under the brand name Ruzurgi for the treatment of Lambert-Eaton myasthenic syndrome (LEMS) in people 6 to less than 17 years of age. Ruzurgi is no longer available in the United States. As of November 2018, the only other treatment approved by the FDA for LEMS (Firdapse) was only approved for use in adults. In 2022, Firdapse approval was expanded to include pediatric patients 6 years of age or older. In 2024, the FDA approved a supplemental New Drug Application increasing the maximum daily dose of Firdapse (amifampridine) for adults and pediatric patients weighing more than 45 kg from 80 mg to 100 mg.