Parasympathomimetic drug

Parasympathomimetic drugs are a type of pharmacological agent that mimic the effects of the parasympathetic nervous system (PNS). They are also known as cholinergic drugs because they stimulate the cholinergic system, which is a part of the PNS that uses acetylcholine (ACh) as its neurotransmitter.

Mechanism of Action

Parasympathomimetic drugs work by either directly stimulating the cholinergic receptor or by inhibiting the enzyme acetylcholinesterase, which breaks down acetylcholine in the synapse. By increasing the levels of acetylcholine, these drugs enhance the activity of the PNS.

Classification

Parasympathomimetic drugs can be classified into two main categories: direct-acting and indirect-acting.

Direct-acting

Direct-acting parasympathomimetic drugs bind directly to and activate the cholinergic receptor. Examples of these drugs include pilocarpine, which is used to treat glaucoma, and bethanechol, which is used to treat urinary retention.

Indirect-acting

Indirect-acting parasympathomimetic drugs inhibit acetylcholinesterase, thereby increasing the amount of acetylcholine available at the synapse. Examples of these drugs include donepezil, used in the treatment of Alzheimer's disease, and neostigmine, used to treat myasthenia gravis.

Clinical Uses

Parasympathomimetic drugs have a wide range of clinical uses, including the treatment of glaucoma, Alzheimer's disease, myasthenia gravis, and various gastrointestinal and urinary disorders. They are also used in ophthalmology to induce miosis, or constriction of the pupil.

Side Effects

The side effects of parasympathomimetic drugs are generally due to overstimulation of the PNS. These can include bradycardia, excessive salivation, bronchoconstriction, diarrhea, and miosis.

See Also

• Parasympatholytic drug
• Sympathomimetic drug
• Sympatholytic drug