Amifampridine 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 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 trade 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 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 U.S. Food and Drug Administration (FDA) approved amifampridine tablets under the trade name Ruzurgi for the treatment of Lambert-Eaton myasthenic syndrome (LEMS) in patients 6 to less than 17 years of age. This is the first FDA approval of a treatment specifically for pediatric patients with LEMS. The FDA granted the approval of Ruzurgi to Jacobus Pharmaceutical.
: 5  In 2007 the drugs international nonproprietary name was published by the WHO.In the face of the seven-year exclusivity that an orphan approval would give to Biomarin, and of the increase in price that would accompany it, Jacobus began racing to conduct formal clinical trials in order to get approval for the free base form before BioMarin; its first Phase II trial was opened in January 2012.In October 2012, while BioMarin had a Phase III trial ongoing in the US, it licensed the US rights to 3,4-DAPP, including the orphan designation and the ongoing trial, to Catalyst Pharmaceuticals. Catalyst anticipated that it could earn $300 to $900 million per year in sales at peak sales for treatment of people with LEMS and other indications, and analysts anticipated the drug would be priced at around. $100,000 in the US. Catalyst went on to obtain a breakthrough therapy designation for 3,4-DAPP in LEMS in 2013, an orphan designation for congenital myasthenic syndromes in 2015 and an orphan designation for myasthenia gravis in 2016.In August 2013, analysts anticipated that FDA approval would be granted to Catalyst in LEMS by 2015.In October 2014, Catalyst began making available under an expanded access program.In March 2015, Catalyst obtained an orphan designation for the use of 3,4-DAPP to treat of congenital myasthenic syndrome.