Individuals who meet any of the following exclusion criteria are not eligible to participate in the study:

• History of epilepsy or seizure.
• Known active brain metastasis.
• Use of Fampridine (4-aminopyridine), and any form of 3,4-diaminopyridine other than the IP provided, such as amifampridine base or Firdapse, during the study.
• Use of medications known to lower the epileptic threshold within 7 days or 5 half-lives.
• Use of medications which inhibit neuromuscular junction function within 7 days or 5 half-lives.
• Use of IVIG, plasmapheresis (plasma exchange), or immunoadsorption within 90 days
• Use of guanidine hydrochloride within 7 days
• Use of rituximab within 12 months
• History of drug allergy to any pyridine-containing substances or any amifampridine phosphate excipient(s).
• Use of any other investigational productwithin 30 days
• Treatment with a concomitant medication that prolongs the QT/QTc interval within 7 days or 5 half-lives.
• Treatment with sultopride (4-amino-N-\[(1-ethylpyrrolidin-2-yl)methyl\]-5-ethylsulfonyl-2-methoxybenzamide) within 7 days.
• An abnormal electrocardiogram (ECG).
• Documented history of arrhythmias.
• History of additional risk factors for torsade de pointes.
• Breastfeeding or pregnant or planning to become pregnant (self or partner) at any time during the study.
• Likely or expected to require treatment for cancer within 3 months (90 days) after entering.
• History of severe renal impairment or evidence of severe renal impairment
• Any condition that places the patient at high risk of poor treatment compliance or of not completing the study.
• History of uncontrolled asthma.