Physostigmine (PSM)

Physostigmine acts by interfering with the metabolism of acetylcholine. It is a covalent (reversible - bond hydrolyzed and released) inhibitor of acetylcholinesterase, the enzyme responsible for the breakdown of acetylcholine in the synaptic cleft of the neuromuscular junction. Physostigmine has two chiral carbon atoms. Therefore, attention needs to be paid to the synthesis of the correct diastereomers. Physostigmine functions as an acetylcholinesterase inhibitor. Its mechanism is to prevent the hydrolysis of acetylcholine by acetylcholinesterase at the transmitted sites of acetylcholine. This inhibition enhances the effect of acetylcholine, making it useful for the treatment of cholinergic disorders and myasthenia gravis. More recently, physostigmine has been used to improve the memory of Alzheimer’s patients due to its potent anticholinesterase activity. However, the drug form of physostigmine, physostigmine salicylate, has poor bioavailability.