FDA Approves First Treatment for Lambert-Eaton Myasthenic Syndrome, A Rare Autoimmune Disorder

FDA News Release. November 28, 2018. Available at: https://www.fda.gov/NewsEvents/Newsroom/PressAnnouncements/ucm627093.htm (accessed 12/4/18).

The US Food and Drug Administration (FDA) has approved amifampridine (Firdapse) tablets as the first ever treatment of the rare autoimmune disorder Lambert-Eaton myasthenic syndrome (LEMS) in adults (1).

In LEMS, the immune system attacks the neuromuscular junction and disrupts the ability of nerve cells to send signals to muscle cells. LEMS may be associated with other autoimmune diseases, but more commonly occurs in patients with cancer such as small cell lung cancer, where its onset precedes or coincides with the diagnosis of cancer. The prevalence of LEMS is estimated to be three per million individuals worldwide.

The efficacy of amifampridine was studied in a pair of clinical trials involved 64 adult patients administered either amifampridine or placebo. Using the 13-item, physician-rated categorial Quantitative Myasthenia Gravis scale to assess for muscle weakness, as well as the seven-point, patient-rated Subject Global Impression, investigators assessed the therapy’s benefit for LEMS’ most prevalent symptoms. For both measures, patients treated with amifampridine reported greater benefits than those administered placebo.

In a statement included with the announced approval, Billy Dunn, MD, director of the Division of Neurology Products in the FDA’S Center for Drug Evaluation and Research, noted the burdens faced by the 3 million-patient population. “There has been a long-standing need for a treatment for this rare disorder,” Dunn said. “Patients with LEMS have significant weakness and fatigue that can often cause great difficulties with daily activities.”

The most common side effects experienced by patients in the clinical trials were burning or prickling sensation (paresthesia), upper respiratory tract infection, abdominal pain, nausea, diarrhea, headache, elevated liver enzymes, back pain, hypertension and muscle spasms. Seizures have been observed in patients without a history of seizures. Because it affects voltage-gated ion channels, it is contraindicated in people with long QT syndrome and in people taking a drug that might prolong QT like sultopride, disopyramide, cisapride, domperidone, rifampicin or ketoconazole. It is also contraindicated in people with epilepsy or badly controlled asthma.