FDA OKs First Treatment for Lambert-Eaton Myasthenic Syndrome

Megan Brooks

November 30, 2018

The US Food and Drug Administration (FDA) has approved amifampridine (Firdapse, Catalyst Pharmaceuticals) 10-mg tablets for the treatment of Lambert-Eaton myasthenic syndrome (LEMS) in adults.

Amifampridine, a potassium channel blocker, is the first FDA-approved treatment for LEMS.

"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 a news release. "Patients with LEMS have significant weakness and fatigue that can often cause great difficulties with daily activities."

LEMS is a rare autoimmune disorder that affects the connection between nerves and muscles and causes weakness and other symptoms in affected patients. LEMS may be associated with other autoimmune diseases but more commonly occurs in patients with small–cell lung cancer. In these patients, its onset precedes or coincides with the diagnosis of cancer. It affects roughly 1 in 100,000 people in the United States.

Amifampridine was evaluated in two phase 3 placebo-controlled clinical trials involving 64 adults. Efficacy was assessed on the basis of scores on the Quantitative Myasthenia Gravis test (a 13-item physician-rated categorical scale assessing muscle weakness) and the Subject Global Impression scale (a 7-point scale on which patients rate their overall impression of the effects of the study treatment on their physical well-being).

Patients treated with amifampridine experienced "rapid, significant and sustained improvements in muscle function, and reduced weakness and fatigability compared to patients receiving placebo. These benefits were observed by both patients and physicians," the company said in a press statement.

The most common side effects were paresthesia, upper respiratory tract infection, abdominal pain, nausea, diarrhea, headache, elevation of liver enzyme level, back pain, hypertension, and muscle spasms.

Seizures have been observed in patients without a history of seizures. Amifampridine is contraindicated in patients who have a history of seizures. Full prescribing information is available online.

Amifampridine is expected to be commercially available early in the first quarter of 2019.

The drug received breakthrough and orphan drug designation and priority review status.

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