Chapter 21: Cholinergic Drugs – The Parasympathetic System

The PNS uses acetylcholine (ACh) as its key neurotransmitter, interacting with two primary types of cholinergic receptors: muscarinic receptors found postsynaptically on effector organs like glands and smooth muscle, and nicotinic receptors located in the ganglia. Cholinergic drugs are classified based on their mechanism of action: direct-acting agents bind and activate the receptors directly, while indirect-acting agents, or cholinesterase inhibitors, increase ACh concentration by blocking the enzyme acetylcholinesterase (AChE) responsible for ACh breakdown. These drugs are clinically applied to areas regulated by the PNS, resulting in effects such as increased gastrointestinal (GI) motility, urinary frequency, miosis, and decreased heart rate. Specific indications include treating urinary retention (e.g., bethanechol), diagnosing and treating myasthenia gravis (e.g., edrophonium, pyridostigmine), and managing symptoms of mild to moderate Alzheimer’s disease using cholinesterase inhibitors like donepezil to enhance memory and learning. A critical nursing focus involves monitoring for adverse effects resulting from parasympathetic overstimulation, known as a cholinergic crisis, which can be summarized by the SLUDGE acronym; the corresponding antidote, atropine sulphate, must be readily available. Furthermore, nurses must educate patients and caregivers that Alzheimer’s treatments are symptomatic, non-curative, and may require up to six weeks to demonstrate therapeutic effects.