What is an example of a cholinergic drug?

October 8, 2025 •

4 min read

Cholinergic drugs work by affecting the neurotransmitter acetylcholine, a primary chemical messenger of the parasympathetic nervous system. A prominent example of a cholinergic drug is pyridostigmine, an indirect-acting agent used to treat conditions like myasthenia gravis.

Quick Summary

Pyridostigmine is an indirect-acting cholinergic drug that treats myasthenia gravis by inhibiting acetylcholinesterase, increasing acetylcholine levels at the neuromuscular junction. This action enhances nerve-muscle communication, improving muscle strength. Other cholinergic drugs vary in their mechanisms and medical uses.

Key Points

Pyridostigmine as an example: Pyridostigmine (Mestinon) is a specific example of an indirect-acting cholinergic drug, known for treating myasthenia gravis.
Mechanism of action: It functions by inhibiting acetylcholinesterase, an enzyme that breaks down acetylcholine, thereby increasing the concentration of this neurotransmitter at nerve-muscle junctions.
Therapeutic effect: In myasthenia gravis, this leads to stronger nerve signals and improved muscle function, counteracting the effects of the autoimmune disease.
Therapeutic uses: Beyond myasthenia gravis, pyridostigmine is also used to reverse neuromuscular blocks and can be used off-label for conditions like POTS.
Side effects: Common side effects are related to excessive parasympathetic stimulation and can include digestive issues, sweating, and increased salivation, but can also lead to more serious conditions like cholinergic crisis.
Categorization: Cholinergic drugs are broadly categorized into direct-acting agents (like bethanechol) that bind directly to receptors and indirect-acting agents (like pyridostigmine) that inhibit the breakdown of acetylcholine.

Understanding Cholinergic Drugs

Cholinergic drugs are a class of medications that mimic or enhance the actions of acetylcholine (ACh), the chief neurotransmitter of the parasympathetic nervous system (PNS). The PNS is responsible for the body's "rest and digest" functions, which include slowing heart rate, increasing glandular secretions, and contracting smooth muscles. By influencing the cholinergic system, these drugs can treat various medical conditions, from neurological disorders to issues with bladder function.

The actions of cholinergic drugs are mediated by two main types of receptors: nicotinic and muscarinic. Nicotinic receptors are located in the neuromuscular junctions and the autonomic nervous system ganglia, while muscarinic receptors are found in target organs such as smooth muscles, glands, and the heart. Based on their mechanism, cholinergic drugs are divided into two main categories: direct-acting and indirect-acting agents.

Direct-acting cholinergic drugs: These agents, such as bethanechol and pilocarpine, bind directly to and activate cholinergic receptors. Bethanechol, for instance, is used to increase bladder and gastrointestinal motility. Pilocarpine is used to constrict pupils and lower intraocular pressure in glaucoma.
Indirect-acting cholinergic drugs: These agents, also known as anticholinesterase inhibitors, work by inhibiting the enzyme acetylcholinesterase (AChE), which is responsible for breaking down acetylcholine in the synaptic cleft. By preventing the breakdown of ACh, these drugs increase the concentration and prolong the action of the neurotransmitter at the receptor sites. This category includes drugs used for myasthenia gravis and Alzheimer's disease.

Pyridostigmine: An Example of a Cholinergic Drug

One of the most well-known and widely used examples of an indirect-acting cholinergic drug is pyridostigmine, which is also sold under the brand name Mestinon. It is primarily used to manage the muscle weakness associated with myasthenia gravis (MG). MG is an autoimmune disorder where the body's own immune system attacks and destroys or blocks the nicotinic acetylcholine receptors at the neuromuscular junction, leading to impaired nerve-muscle communication.

How Pyridostigmine Works in Myasthenia Gravis

Pyridostigmine is a reversible acetylcholinesterase inhibitor. Its mechanism is as follows:

Inhibition of AChE: Pyridostigmine binds to the acetylcholinesterase enzyme, temporarily deactivating it.
Increased ACh availability: By inhibiting AChE, pyridostigmine prevents the rapid hydrolysis (breakdown) of acetylcholine.
Enhanced nerve transmission: The resulting higher concentration of acetylcholine in the synaptic cleft means there are more ACh molecules available to bind to the remaining functional receptors on the muscle cells.
Improved muscle function: This enhanced binding of ACh strengthens the signal between the nerves and muscles, leading to improved muscle contraction and reduced symptoms of muscle weakness and fatigue.

Unlike some other anticholinesterase agents, pyridostigmine does not readily cross the blood-brain barrier, which minimizes its central nervous system effects. This makes it particularly suitable for treating peripheral conditions like MG.

Therapeutic Uses Beyond Myasthenia Gravis

While its primary indication is MG, pyridostigmine has other medical uses:

Reversal of neuromuscular block: It can be used in a hospital setting to reverse the effects of certain muscle relaxants (nondepolarizing neuromuscular blockers) used during surgery.
Postural orthostatic tachycardia syndrome (POTS): It is sometimes used off-label to treat symptoms of POTS, a condition that causes a rapid increase in heart rate when standing.
Protection against nerve agents: In a military context, pyridostigmine has been approved for use as a pretreatment against exposure to nerve gas agents like soman.

Side Effects and Considerations

Since pyridostigmine promotes cholinergic activity, its side effects are typically a result of excessive parasympathetic stimulation, which can be remembered using the mnemonic SLUDGE-M:

Salivation (increased)
Lacrimation (tearing)
Urination (frequent and urgent)
Defecation (diarrhea)
Gastrointestinal cramping
Emesis (vomiting)
Miosis (pupil constriction) and Muscle twitching (fasciculations)

More serious side effects can include severe muscle weakness (a "cholinergic crisis"), difficulty breathing, or severe allergic reactions. The drug is contraindicated in patients with mechanical intestinal or urinary obstruction.

Comparison of Cholinergic Drug Types


Feature	Direct-Acting Cholinergic Drugs	Indirect-Acting Cholinergic Drugs (Anticholinesterase Inhibitors)
Mechanism of Action	Directly bind to and activate acetylcholine receptors.	Inhibit the enzyme acetylcholinesterase, thereby increasing acetylcholine concentration.
Examples	Bethanechol, Pilocarpine, Carbachol.	Pyridostigmine, Neostigmine, Donepezil.
Therapeutic Uses	Urinary retention, glaucoma, xerostomia (dry mouth).	Myasthenia gravis, Alzheimer's disease, reversal of neuromuscular block.
Duration of Action	Varies, but can be longer than endogenous acetylcholine.	Reversible inhibition generally results in effects lasting several hours.
Primary Effect	Activates cholinergic receptors on specific effector organs.	Enhances the effect of naturally released acetylcholine.

Conclusion

Cholinergic drugs, which work by mimicking or enhancing the action of acetylcholine, play a vital role in modern medicine. A classic example of a cholinergic drug is pyridostigmine, an indirect-acting agent that has revolutionized the treatment of myasthenia gravis by boosting acetylcholine levels at the neuromuscular junction. By inhibiting acetylcholinesterase, it improves nerve-muscle communication and mitigates debilitating muscle weakness. Understanding the specific mechanisms and side effects of drugs like pyridostigmine is essential for effective treatment and patient safety. For additional pharmacological details, authoritative resources such as the National Institutes of Health provide comprehensive overviews.

Frequently Asked Questions

Pyridostigmine is primarily used to treat the symptoms of myasthenia gravis, a neuromuscular disease that causes muscle weakness. It can also be used to reverse the effects of certain muscle relaxants after surgery.

Pyridostigmine is an indirect-acting cholinergic drug. It works by inhibiting the enzyme acetylcholinesterase, which normally breaks down acetylcholine. By blocking this enzyme, pyridostigmine increases the level of acetylcholine available to stimulate receptors and improves nerve-muscle signaling.

Direct-acting cholinergic drugs bind directly to and activate acetylcholine receptors, while indirect-acting drugs (like pyridostigmine) increase acetylcholine levels by inhibiting the enzyme that breaks it down.

Common side effects include nausea, diarrhea, stomach cramps, increased salivation, and muscle cramps. These are typically related to increased cholinergic activity. In higher doses, more severe effects can occur.

A cholinergic crisis is a rare but serious condition caused by excessive cholinergic drug activity, leading to symptoms like extreme muscle weakness (including breathing difficulties), nausea, vomiting, and diarrhea. It requires immediate medical attention.

Yes, aside from its main use in myasthenia gravis, pyridostigmine can be used to reverse neuromuscular blocks and is sometimes used off-label to treat postural orthostatic tachycardia syndrome (POTS).

You should not take pyridostigmine if you have a mechanical intestinal or urinary obstruction. Caution is also advised for patients with asthma, epilepsy, and certain heart conditions. Alcohol should be avoided as it can increase drowsiness.