Amifampridine (Firdapse), currently approved in the European Union, is the first and only approved drug for the symptomatic treatment of Lambert-Eaton Myasthenic Syndrome (LEMS) in adults, a rare autoimmune disease with the primary symptoms of muscle weakness. In LEMS, the body’s own immune system attacks connections between nerves and muscles and disrupts the ability of nerve cells to send signals to muscle cells. Amifampridine blocks voltage-dependent potassium channels, thereby prolonging pre-synaptic cell membrane depolarization. Prolonging the action potential enhances the transport of calcium into the nerve ending. The resulting increase in intracellular calcium concentrations facilitates exocytosis of acetylcholine containing vesicles, which in turn enhances neuromuscular transmission. Amifampridine phosphate has been granted Orphan Drug Designation and Breakthrough Therapy designation by the FDA for the treatment of Lambert-Eaton Myasthenic Syndrome (LEMS).

Dalfampridine is a potassium channel blocker, used as a research tool in characterizing subtypes of the potassium channel. Dalfampridine has also been used as a drug, to manage some of the symptoms of multiple sclerosis, and is indicated for symptomatic improvement of walking in adults with several variations of the disease. The mechanism by which dalfampridine exerts its therapeutic effect has not been fully elucidated. Dalfampridine is a broad spectrum potassium channel blocker. In animal studies, dalfampridine has been shown to increase conduction of action potentials in demyelinated axons through inhibition of potassium channels.