Prolonged-release fampridine (4-aminopyridine) is a voltage-gated potassium channel blocking agent. It relieves conduction block in demyelinated nerve fibers by blocking voltage-gated potassium channels on the paranodal axon membranes in vitro. It enhances synaptic transmission by blocking repolarizing potassium currents thus increasing the size of the presynaptic action potential and thus increasing transmitter release. It has been shown in multiple sclerosis patients to improve walking capabilities as measured by the timed 25 feet walk test by more than 20% in approximately 34% of subjects. Prolonged-release fampridine also has measurable effects on motor evoked potentials with transcranial magnetic stimulation in patients with multiple sclerosis and partial spinal cord injuries.