Cholinergics
Cholinergics mimic the parasympathetic neurotransmitter acetylcholine.
Acetylcholine (Ach) is a neurotransmitter located in the ganglions and terminal
nerve endings of parasympathetic nerves that connect to receptors in organs,
tissues, and glands.
There are two types of cholinergic receptors. These are muscarinic receptors
and nicotinic receptors. Muscarinic receptors stimulate smooth muscles and slow
the heart rate. Nicotinic receptors affect skeletal muscles. Some cholinergic med-
ications are selective and affect either muscarinic receptor or nicotinic receptors
while other cholinergic medications are non-specific and affect both receptors.
Direct-acting cholinergics act on the receptors to activate a tissue response.
Indirect-acting cholinergic drugs inhibit the action of cholineresterase (acetyl-
cholinesterase) by forming a chemical complex that permits acetylcholine to per-
sist and attach to the receptor. These drugs are called cholinesterase inhibitors
or anticholinesterase drugs.
Pilocarpine is a commonly used direct-acting cholinergic that is used to treat
glaucoma. Pilocarpine reduces intraocular pressure by constricting pupils and
opening the Canal of Schlemm enabling aqueous humor (fluid) to drain.
There are two types of cholinesterase inhibitors. These are reversible inhibitors
and irreversible inhibitors. A reversible inhibitor binds to the cholinesterase
enzyme for a period of time and then unbinds enabling the cholinesterase enzyme
to properly function. An irreversible inhibitor permanently binds to the cholin-
esterase enzyme.
Cholinergics stimulate (see chart) the bladder, constrict pupils (miosis),
increase neuromuscular transmission, and provide muscle tone to the GI tract.
Other effects include a decreased heart rate and blood pressures while increas-
ing secretion of the salivary glands.
See direct-acting cholinergic list is provided in the Appendix. Detailed tables
show doses, recommendations, expectations, side effects, contraindications, and
more; available on the book’s Web site (see URL in Appendix).
Anticholinergics
Anticholinergics drugs (see chart) inhibit acetylcholine by occupying the acetyl-
choline receptors. Anticholinergics are also called parasympatholytics, choliner-
gic blocking agents, cholinergic or muscarinic antagonists, antiparasympathetic
agents, antimuscarinic agents, or antispasmodics.
CHAPTER 15 Nervous System Drugs^287