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Firdapse® (amifampridine) is one of the first drugs to be approved for the treatment of Lambert-Eaton myasthenic syndrome (LEMS) in adults.
The drug was developed by BioMarin Pharmaceutical and is marketed by Catalyst Pharmaceutical, which secured the marketing rights to Firdapse® in North America under a $5m deal in October 2012. The EU rights are retained by BioMarin.
The European Commission (EC) granted marketing authorisation (MA) to Firdapse® for the symptomatic treatment of LEMS in December 2009. The drug also secured orphan drug designation in the EU.
The US Food and Drug Administration (FDA) granted breakthrough therapy designation to the drug in August 2013. Catalyst Pharmaceutical submitted a new drug application (NDA) for Firdapse® to the FDA in March 2018, and the application was accepted and granted priority review status in May of the same year.
Firdapse® was approved by the FDA in November 2018.
Lambert-Eaton myasthenic syndrome causes and symptoms
LEMS is a rare autoimmune disorder that occurs when an individual’s immune system attacks its own tissues, particularly at the neuromuscular junction. The condition hampers the nerve cells’ ability to transmit signals to the muscle cells, causing muscle weakness.
The disease was named after the neurologists Edward Lambert and Lee Eaton, who first described the disease during 1950s and 1960s.
The condition affects three in one million individuals worldwide. An estimated 50% to 60% of LEMS patients also suffer from an underlying cancer such as small cell lung cancer.
The most common symptoms of the disease are weakness in the limbs and eye muscles, fatigue, and difficulty talking and swallowing.
Firdapse’s mechanism of action
Firdapse® is a voltage-dependent potassium channel blocker that is known to prolong the depolarisation of the cell membrane and inhibit repolarisation, thus helping to open slow voltage-dependent calcium channels.
The action results in increased calcium transportation into the nerve endings. The higher concentration of intra-cellular calcium improves neuromuscular transmission thereby improving muscular strength.
Firdapse® is available in the form of white, round 10mg tablets intended for oral administration.
Clinical trials on Firdapse
The FDA’s approval of Firdapse® was based on the positive results of two Phase III randomised, double-blind, placebo-controlled clinical studies named Study-1 (NCT01377922) and Study-2 (NCT02970162).
The trials enrolled a total of 64 adult patients with LEMS. The co-primary endpoints of the study were the change in the quantitative myasthenia gravis (QMG) score and the subject global impression (SGI) score.
In Study-1, a total of 38 patients were randomised to receive either Firdapse® or placebo for more than seven days. The QMG score in patients receiving Firdapse® reached significant p-value of 0.045, while the p-value in SGI score was 0.003.
In Study-2, 26 patients were randomised to either remain in the Firdapse® treatment group or switch to placebo for four days. The QMG score in patients treated with Firdapse® reached p-value of 0.0004, while the p-value in SGI score was 0.0003.
A difference of 6.4 points in the QMG endpoint was noted between patients treated with Firdapse® and placebo. The drug was well tolerated by patients and the safety profile was similar to previous studies.
The most common side effects reported by patients during the clinical trials were paraesthesia, diarrhoea, upper respiratory tract infection, pain in the abdomen, nausea, headache, increased liver enzymes, back pain, high blood pressure and muscle spasms.
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