Neostigmine belongs to the group of medicines called anticholinesterases. It works by prolonging the action acetylcholine, which is found naturally in the body. It does this by inhibiting the action of the enzyme acetylcholinesterase. Acetylcholine stimulates a type of receptor called muscarinic receptors. When stimulated, these receptors have a range of effects. Chemically, neostigmine bromide is (m-hydroxyphenyl)trimethylammonium bromide dimethylcarbamate. It is a white, crystalline, bitter powder, soluble 1:1 in water, with a molecular weight of 303.20.
Muscarinic receptors are found throughout the body, especially on muscle. Stimulation of these receptors causes to muscle contraction. In myasthenia gravis the body's immune system destroys many of the muscarinic receptors, so that the muscle becomes less responsive to nervous stimulation. Neostigmine bromide increases the amount of acetylcholine at the nerve endings. Increased levels of acetyl choline allow the remaining receptors to function more efficiently. This medicine usually restores mucle function to near-normal levels.
Neostigmine inhibits the activity of the enzyme cholinesterase, which breaks up acetylcholine, a neurotransmitter involved in muscle activity. Consequently, neostigmine increases the amount of available acetylcholine, which in turn improves muscle strength and endurance in patients with milder forms of myasthenia gravis. The drug's effect also improves the tone of the muscles controlling bladder or bowel activity.
Neostigmine inhibits the hydrolysis of acetylcholine by competing with acetylcholine for attachment to acetylcholinesterase at sites of cholinergic transmission. It enhances cholinergic action by facilitating the transmission of impulses across neuromuscular junctions. It also has a direct cholinomimetic effect on skeletal muscle and possibly on autonomic ganglion cells and neurons of the central nervous system. Neostigmine undergoes hydrolysis by cholinesterase and is also metabolized by microsomal enzymes in the liver. Protein binding to human serum albumin ranges from 15 to 25 percent.