The Food and Drug Administration (FDA) recently approved amifampridine (Ruzurgi), the first drug to treat Lambert-Eaton myasthenic syndrome (LEMS) in children ages six to 16 years. LEMS is a rare autoimmune disorder that occurs when antibodies interfere with electrical impulses between the nerve and muscle cells. Symptoms include muscle weakness, a tingling sensation in the affected areas, fatigue, and dry mouth.

According to the FDA, although the prevalence of LEMS in children is unknown, its overall prevalence is estimated to be three per 1 million people worldwide. The efficacy trial for amifampridine was a randomized, double-blind, placebo-controlled withdrawal study that included 32 adults and no children (drug studies are rarely done in children and this condition is extremely rare). Patients were stabilized on a dose of amifampridine for at least three months prior to entering the study; at that point, patients who continued with amifampridine were compared with patients who switched to placebo, the latter reporting greater muscle weakness than those who remained on the drug.

Amifampridine can cause seizures and severe hypersensitivity reactions. The drug is contraindicated in patients with a history of either of these adverse effects. If amifampridine is prescribed concomitantly with drugs that lower the seizure threshold, the risk of seizures is increased. The most common adverse effects (seen in at least 10% of patients) include paresthesia/dysesthesia, abdominal pain, dyspepsia, dizziness, and nausea.

Patients should be assessed for a history of seizures. If seizures occur, patients should contact their health care provider to discuss temporary or permanent discontinuation of the drug. If anaphylaxis occurs, the drug should be discontinued.

For complete prescribing information for amifampridine, see http://www.accessdata.fda.gov/drugsatfda_docs/label/2019/209321s000lbl.pdf.