Effect of Amifampridine on Neuromuscular Transmission in Patients Treated With OnabotulinumtoxinA

Inclusion Criteria: * Age: 18-80 years of either gender and of any racial background * Underwent BTX-A injection of facial muscles including frontalis with a total dose between 100-200 units between 80 and 150 days prior to study * Have decision-making capacity to provide informed consent to study drug dosing and Single Fiber Electromyography (SFEMG) Exclusion Criteria: * History of cardiac arrhythmia * History of seizures or uncontrolled asthma * History of renal or hepatic disease * History of any generalized neuromuscular disease * History of Bell's Palsy or facial nerve trauma * History of treatment with or sensitivity to amifampridine, 3,4 diaminopyridine (DAP) or 4-aminopyridine (Ampyra®) * Currently experiencing sequelae of previous BTX-A treatment * Current use of pyridostigmine (known to alter neuromuscular transmission) * Use of any investigational drug or device within 30 days of enrollment