Public health agency The US Food and Drug Administration Wednesday authorised the approval of Firdapse (amifampridine) tablets under its orphan drug designation, priority review and breakthrough therapy designations for the treatment of Lambert-Eaton myasthenic syndrome (LEMS), a rare autoimmune disorder.

This US FDA's approval of Firdapse was awarded to Catalyst Pharmaceuticals Inc.

Additionally, the Firdapse (amifampridine) tablets is the first US FDA approval for the treatment of LEMS in adults.

In people with LEMS, the body's own immune system attacks the neuromuscular junction (the connection between nerves and muscles) 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 company said the efficacy of Firdapse was studied in two clinical trials that together included 64 adult patients who received Firdapse or placebo.

According to the company, the studies measured the Quantitative Myasthenia Gravis score (a 13-item physician-rated categorical scale assessing muscle weakness) and the Subject Global Impression (a seven-point scale on which patients rated their overall impression of the effects of the study treatment on their physical well-being). For both measures, the patients receiving Firdapse experienced a greater benefit than those on placebo.