Mechanism of Action: Pyridostigmine exerts its effects by competing with acetylcholine for its binding site on acetylcholinesterase. By interfering with acetylcholine enzymatic destruction, pyridostigmine potentiates the action of acetylcholine on both the skeletal muscle (nicotinic receptor) and the GI tract (muscarinic receptor). Pyridostigmine also can stimulate cholinergic responses in the eyes (causing miosis) if directly applied. Different muscle groups exhibit different levels of response to anticholinesterase agents, and doses that produce stimulation of one muscle group can cause weakness, through overdose, in responses to cholinesterase inhibitors include: increased skeletal muscle tone (nicotinic); increased gastric motility and GI tone (muscarinic); bradycardia (muscarinic); ureteral constriction (muscarinic); stimulation of the sweat and salivary glands (muscarinic); and constriction of the bronchi (muscarinic). There is also some evidence that they have a direct action on skeletal muscle.
Pyridostigmine (Mestinon) is an oral cholinesterase inhibitor. Acetylcholine is one of many neurotransmitters in our bodies. Neurotransmitters are chemicals that help our cells communicate with each other. Depending on the organ that it acts upon, acetylcholine produces different effects. One important function of acetylcholine is to produce muscle contractions and movement. In people with myasthenia gravis or people treated with neuromuscular blocking medicines there is a decrease in the levels of acetylcholine. In such cases pyridostigmine may be used to increase acetylcholine levels and improve muscle contraction or movement. Pyridostigmine increases the concentration of acetylcholine at nerve junctions by inhibiting cholinesterase, the enzyme that destroys acetylcholine.