By directly stimulating cholinergic receptors,
cholinergic agonists mimic the action of the neurotransmitter acetylcholine.
They include such drugs as:
The action and metabolism of cholinergic agonists
vary widely and depend on the affinity of the individual drug for muscarinic or
Cholinergic agonists rarely are administered by
I.M. or I.V. injec-tion because they’re almost immediately broken down by
cholin-esterases in the interstitial spaces between tissues and inside the
blood vessels. Moreover, they begin to work rapidly and can cause a cholinergic
crisis (a drug overdose resulting in extreme muscle weakness and possibly
paralysis of the muscles used in respira-tion).
Cholinergic agonists are usually administered:
topically, with eye drops
by subcutaneous (subQ) injection.
SubQ injections begin to work more rapidly
than oral doses.
All cholinergic agonists are metabolized by
at the muscarinic and nicotinic receptor sites
in the plasma (the liquid portion of the blood)
in the liver.
All drugs in this class are excreted by the
Cholinergic agonists work by mimicking the action
of acetylcho-line on the neurons in certain organs of the body called target or-gans. When they combine with
receptors on the cell membranesof target organs, they stimulate the muscle and
bradycardia (a slow heart rate)
dilation of blood vessels
constriction of the bronchioles
increased activity of the GI tract
increased tone and contraction of the bladder muscles
constriction of the pupils.
Cholinergic agonists are used to:
§ treat atonic (weak) bladder conditions and
postoperative and postpartum urine retention
§ treat GI disorders, such as postoperative
abdominal distention and GI atony
§ reduce eye pressure in patients with glaucoma
and during eye surgery
§ treat salivary gland hypofunction caused by
radiation therapy or Sjögren’s syndrome.
Cholinergic agonists have specific interactions
with other drugs.
Examples include the following:
· Other cholinergic drugs, particularly anticholinesterase drugs (such as
ambenonium, edrophonium, neostigmine, physostigmine, and pyridostigmine), boost
the effects of cholinergic agonists and increase the risk of toxicity.
Cholinergic blocking drugs (such as atropine, belladonna, ho-matropine,
methantheline, methscopolamine, propantheline, and scopolamine) reduce the
effects of cholinergic drugs.
Quinidine also reduces the effectiveness of cholinergic agonists. (See Adverse reactions to cholinergic agonists.)