Edrophonium is a readily reversible acetylcholinesterase inhibitor

Acetylcholinesterase inhibitor

An acetylcholinesterase inhibitor or anti-cholinesterase is a chemical that inhibits the cholinesterase enzyme from breaking down acetylcholine, increasing both the level and duration of action of the neurotransmitter acetylcholine.- Uses :Acetylcholinesterase inhibitors:* Occur naturally as...

. It prevents breakdown of the neurotransmitter

Neurotransmitter

Neurotransmitters are endogenous chemicals that transmit signals from a neuron to a target cell across a synapse. Neurotransmitters are packaged into synaptic vesicles clustered beneath the membrane on the presynaptic side of a synapse, and are released into the synaptic cleft, where they bind to...

 acetylcholine

Acetylcholine

The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...

 and acts by competitively inhibiting the enzyme acetylcholinesterase

Acetylcholinesterase

"Acetylcholinesterase, also known as AChE or acetylcholine acetylhydrolase, is an enzyme that degrades the neurotransmitter acetylcholine, producing choline and an acetate group. It is mainly found at neuromuscular junctions and cholinergic nervous system, where its activity serves to terminate...

, mainly at the neuromuscular junction

Neuromuscular junction

A neuromuscular junction is the synapse or junction of the axon terminal of a motor neuron with the motor end plate, the highly-excitable region of muscle fiber plasma membrane responsible for initiation of action potentials across the muscle's surface, ultimately causing the muscle to contract...

. It is sold under the trade names Tensilon, Enlon and Reversol.

Clinical uses

Indication: edrophonium (by the so-called Tensilon test) is used to differentiate myasthenia gravis

Myasthenia gravis

Myasthenia gravis is an autoimmune neuromuscular disease leading to fluctuating muscle weakness and fatiguability...

 from cholinergic crisis

Cholinergic crisis

A cholinergic crisis is an over-stimulation at a neuromuscular junction due to an excess of acetylcholine , as of a result of the inactivity of the AChE enzyme, which normally breaks down acetylcholine. This is a consequence of some types of nerve gas,...

. In myasthenia gravis, where a person is not able to produce enough neuromuscular

Nicotinic acetylcholine receptor

Nicotinic acetylcholine receptors, or nAChRs, are cholinergic receptors that form ligand-gated ion channels in the plasma membranes of certain neurons and on the postsynaptic side of the neuromuscular junction...

 stimulation, edrophonium will reduce the muscle weakness by effectively supplying more acetylcholine

Acetylcholine

The chemical compound acetylcholine is a neurotransmitter in both the peripheral nervous system and central nervous system in many organisms including humans...

. In a cholinergic crisis, where a person has too much neuromuscular

Nicotinic acetylcholine receptor

Nicotinic acetylcholine receptors, or nAChRs, are cholinergic receptors that form ligand-gated ion channels in the plasma membranes of certain neurons and on the postsynaptic side of the neuromuscular junction...

 stimulation, edrophonium will make the muscle weakness worse by inducing a depolarizing block.

Chemistry

Edrophonium, ethyl-(3-hydroxyphenyl)dimethylammonium chloride, is made by reacting 3-dimethylaminophenol with ethyl bromide, which forms ethyl(3-hydroxyphenyl)dimethylammonium bromide, the bromine atom of which is replaced with a chlorine atom by reacting it with silver chloride

Silver chloride

Silver chloride is a chemical compound with the chemical formula AgCl. This white crystalline solid is well known for its low solubility in water . Upon illumination or heating, silver chloride converts to silver , which is signalled by greyish or purplish coloration to some samples...

, giving edrophonium.

• J.A. Aeschlimann, A. Stempel, (1953).

Sources

1. Brenner, G. M. (2000). Pharmacology. Philadelphia, PA: W.B. Saunders Company. ISBN 0-7216-7757-6
2. Canadian Pharmacists Association (2000). Compendium of Pharmaceuticals and Specialties (25th ed.). Toronto, ON: Webcom. ISBN 0-919115-76-4