A therapy that European regulators approved for treating Lambert-Eaton myasthenic syndrome (LEMS) can help manage myasthenia gravis symptoms, a study reports.
The findings on Firdapse appeared in the Journal of Clinical Neuroscience. The title of the article is “3,4-Diaminopyridine for the treatment of myasthenia gravis with electrophysiological patterns of Lambert-Eaton myasthenic syndrome.”
Myasthenia gravis and LEMS are autoimmune disorders that share a common cause — abnormal interaction between nerve cells and muscles. This is due to overproduction and accumulation of antibodies that block communication signals.
Doctors can often distinguish between the two disorders. One reason is that in many cases, they have different manifestations. They also respond differently to stimulation and to cholinesterase inhibitors — a standard treatment for muscle disorders.
But some patients have characteristics of both diseases, posing a diagnostic and treatment challenge.
Firdapse (3,4-Diaminopyridine, 34DAP) is a drug approved in Europe for the treatment of LEMS.
South Korean researchers decided to see if Firdapse could help eight myasthenia gravis patients who also had some features of LEMS. All of the participants had had limited benefits from standard strategies, including immunosuppressive drugs, plasma exchange, removal of the thymus, and Mestinon (pyridostigmine).
The first step in the study was taking patients off Mestinon. After receiving an injection of Prostigmin (neostigmine), the patients then took Firdapse four times a day for two days. Then they received a combination of Firdapse and Mestinon for two days, with doses adjusted to match patients’ ability to tolerate the combo.
Between each treatment, researchers performed several tests to gauge patients’ response.
One measure was quantitative myasthenia gravis score , which tracks the severity of the disease. Prostigmin reduced patients’ scores from the start of the study by 3.7 points and Firdapse by 3.9 points. The best response was with the combo therapy — a 6.1-point reduction.
Another finding was that patients responded better to stimulation when taking Firdapse or the combo therapy than with Prostigmin.
Seven of the eight patients stayed on the combo after the initial study period. The follow-up treatment last three years, with patients’ doses adjusted during that time.
Adding Firdapse to the treatment regimen helped five of the patients perform daily tasks better. Two patients experienced little improvement and discontinued the treatment. Two who improved after a year discontinued Firdapse as well.
Collectively, the findings showed that a combination of Firdapse and Mestinon generated the best outcomes. Also, there were “no significant side effects” from long-term use of the therapy, the researchers wrote. This suggests that Firdapse could be a safe and effective treatment for myasthenia gravis.
Studies with larger groups should done to confirm that Firdapse can help myasthenia gravis patients, researchers added.