Pyridostigmine

Pyridostigmine is a parasympathomimetic and a reversible cholinesterase inhibitor. Since it is a quaternary amine, it is poorly absorbed in the gut and doesn't cross the blood-brain barrier.

Mode of action

In order to understand the mode of action, a quick outline of a synapse is given below. For more information, look up synapse.

Action potentials are conducted along motor nerves to their terminals where they initiate a Ca2+ influx and the release of acetylcholine (ACh). The ACh diffuses across the synaptic cleft and binds to receptors on the post synaptic membrane, causing an influx of Na+ and K+ ions, resulting in depolarisation. If large enough, this depolarisation results in an action potential. In order to prevent constant stimulation once the ACh is released, an enzyme called acetylcholinesterase is present in the endplate membrane close to the receptors on the post synaptic membrane, and quickly hydrolises ACh.

Pyridostigmine inhibits acetylcholinesterase in the synaptic cleft, thus slowing down the hydrolysis of acetylcholine.

Clinical uses

Pyridostigmine is used to treat muscle weakness in people with myasthenia gravis and to combat the effects of curariform drug toxicity. It also has a military use as a nerve gas antidote (it has been used in particular during the first Gulf War).

Pyridostigmine bromide is available under the trade names Mestinon® (Valeant Pharmaceuticals) and Regonol®.

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