4-Aminopyridine

Overview
4-Aminopyridine is prepared by the decarbonylation of pyridine-4-carboxyamide.

Pharmaceutical applications
It has been used clinically in Lambert-Eaton myasthenic syndrome and multiple sclerosis because by blocking potassium channels it prolongs action potentials thereby increasing transmitter release at the neuromuscular junction and elsewhere.

The drug, known as Neurelan, has been shown to reverse tetrodotoxin toxicity in animal experiments.

It is also marketed as Fampridine by Acorda for the treatment of multiple sclerosis, for which it is now in Phase II clinical trials.

4-aminopyridine is marketed as an avicide under the trade name Avitrol. In this treatment it causes convulsions and sometimes death, depending on dosage. Because other members of a flock sometimes are frightened away by poisoned birds, it is described as a bird "frightening agent".

Multiple Sclerosis
4-Aminopyridine (4-AP) is a drug shown to improve visual function and motor skills and relieve fatigue in patients with Multiple Sclerosis (MS). 4-AP is most effective in patients with the chronic progressive form of MS, in patients who are temperature sensitive, and in patients who have had MS for longer than three years. Common side effects include dizziness, nervousness and nausea, and the incidence of adverse effects was shown to be less than 5% in all studies.

4-AP works as a potassium channel blocker. Electrophysiologic studies of demyelinated axons show that abnormal potassium currents decrease action potential duration and amplitude and contribute to conduction failure. Potassium channel blockade prolongs the depolarization phase of the action potential, increasing conductivity along the demyelinated axon.

MS patients treated with 4-AP exhibited a response rate of 29.5% to 80%. A long-term study (32 months) indicated that 80-90% of patients who initially responded to 4-AP exhibited long-term benefits. Although improving symptoms, 4-AP does not inhibit progression of MS.

Spinal cord injury patients have also seen improvement with 4-AP therapy. These improvements include sensory, motor and pulmonary function, with a decrease in spasticity and pain. .

Overdose
Conditions associated with overdose have included parasthesias and seizures. , and atrial fibrillation.