Myasthenia Gravis (MG) is a progressive autoimmune disorder which results in the weakening of muscles. Most people with the condition are able to manage their symptoms with treatment and have a normal life expectancy. However, rare forms of the disease such as MuSK antibody positive MG are more severe and have fewer effective treatment options.
15% of people with MG have the seronegative (SN) form of the condition. 40-50% of individuals with SNMG have the anti-MuSK antibody. The MuSK protein is necessary for maintaining proper neuromuscular junction. This form of MG is most prevalent in females. It’s characterized by a high involvement of the bulbar and cranial muscles and the high frequency of respiratory crises that these patients experience. Individuals are treated with immunosuppressants or anticholinesterase inhibitors however many people with MuSK-MG are resistant to treatment.
Catalyst Pharmaceuticals has just announced positive results from their Phase IIb trial investigating Firdapse (amifampridine phosphate) as a treatment for this unique form of the condition.
Firdapse is a potassium channel blocker which is administered orally in 10mg tablets. The drug works to depolarize the presynaptic membrane. It then slows or inhibits repolarization. This allows the body to open Ca2+ channels and release a greater amount of Acetylcholine, which ultimately can improve neuromuscular transmission. As a result, the patient should experience an improvement in overall muscle function. This drug has already been approved in both the European Union and the United States for the treatment of Lambert-Eaton Myasthenic Syndrome.
Catalyst’s trial was randomized and double-blind. It showed both safety and efficacy of Firdapse for the treatment of MuSK-MG patients. Results from this trial were announced soon after its completion but the comprehensive data from the study has now been made available online. You can read the full report published in SAGE Open Medicine, here.
Catalyst is now working on a Phase 3 trial for the drug at multiple trial sites.
“If our Phase 3 trial is successful, we hope that Catalyst will be able to offer physicians and patients alternatives in the treatment of MuSK-MG.”
You can read more about this trial and Catalyst’s work for MuSK-MG patients here.