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FDA Approves Firdapse, First Treatment for Lambert-Eaton Myasthenic Syndrome
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The FDA has approved amifampridine tablets for the treatment of adult patients with Lambert-Eaton myasthenic syndrome, according to a press release.
Characterized by autonomic changes, depressed tendon reflexes, post-tetanic potentiation and proximal muscle weakness, Lambert-Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder of the neuromuscular junction, affecting approximately three people per million worldwide.
“There has been a long-standing need for a treatment for this rare disorder,” Billy Dunn, MD, director of the Division of Neurology Products in the FDA’s Center for Drug Evaluation and Research, said in the release. “Patients with LEMS have significant weakness and fatigue that can often cause great difficulties with daily activities.”
As the first FDA-approved drug for this disorder, amifampridine (Firdapse, Catalyst Pharmaceuticals) — a potassium channel inhibitor — is intended to prolong nerve signals, permitting greater stimulation of the muscle.
Although LEMS may be associated with other autoimmune diseases, it is regarded as a paraneoplastic syndrome since approximately 60% of patients with LEMS are later diagnosed with an underlying malignancy, most commonly small-cell lung cancer.
The FDA based its approval on two efficacy trials of 64 adult patients, randomized to receive either amifampridine or placebo. The two studies evaluated the quantitative myasthenia gravis score as well as the self-reported Patient Global Impression of Change, in which patients rated their overall impression of the effects of treatment on their physical well-being; in both measures, patients who received amifampridine reported a greater benefit than patients who received placebo.
According to the FDA, the most common adverse events associated with amifampridine in clinical trials were abdominal pain, back pain, diarrhea, elevated liver enzymes, headache, hypertension, muscle spasms, nausea, paresthesia and upper respiratory tract infections; additionally, seizures were reported among patients who lacked a history of seizures.