Also called Cholinomimetic or parasympathomimetic
Cholinomimetic drugs can elicit some or all of the effects
that acetylcholine (ACh) produces.
This class of drugs includes agents that act directly as
agonists at cholinoreceptors and agents that act
indirectly by inhibiting the enzymatic destruction of
The directly acting cholinomimetics can
be subdivided into
Agents that exert their effects primarily through
stimulation of muscarinic receptors at
parasympathetic neuroeffector junctions
(parasympathomimetic drugs) and
Agents that stimulate nicotinic receptors in
autonomic ganglia and at the neuromuscular
Pharmacological Effects of Muscarinic
ACh has four primary effects on the cardiovascular system:
Decrease in cardiac rate (the negative chronotropic effect),
Decrease in the rate of conduction in the specialized tissues of the SA
and atrioventricular (AV) nodes (the negative dromotropic effect), and
Decrease in the force of cardiac contraction (the negative
The last effect is of lesser significance in ventricular than in atrial muscle.
Certain of the above responses can be obscured by baroreceptor and other
reflexes that dampen or counteract the direct responses to ACh.
GASTROINTESTINAL AND URINARY
Although stimulation of vagal input to the gastrointestinal
(GI) tract increases tone, amplitude of contraction, and
secretory activity of the stomach and intestine.
such responses are inconsistently seen with administered
Poor perfusion of visceral organs and rapid hydrolysis by
plasma butyrylcholinesterase limit access of systemically
administered ACh to visceral muscarinic receptors.
Parasympathetic sacral innervation causes detrusor muscle
contraction, increased voiding pressure, and ureter
peristalsis, but for similar reasons these responses are not
evident with administered ACh.
ACh and its analogs stimulate secretion by all glands
that receive parasympathetic innervation, including
the lacrimal, tracheobronchial, salivary, and digestive
The effects on the respiratory system, in addition to
increased tracheobronchial secretion, include
bronchoconstriction and stimulation of the
chemoreceptors of the carotid and aortic bodies.
When instilled into the eye, muscarinic agonists
Cholinergic receptor agonists can be
divided into two groups:
(1) ACh and several synthetic choline
(2) The naturally occurring
The therapeutic usefulness of ACh is limited by
(1) its lack of selectivity as an agonist for different
types of cholinoreceptors and
(2) its rapid degradation by cholinesterases.
These limitations have been circumvented in part by
the development of three choline ester derivatives of
Methacholine differs from ACh only in the addition of
a methyl group at the beta-carbon of ACh.
This modification greatly increases its selectivity for
muscarinic receptors relative to nicotinic receptors.
It renders methacholine resistant to the pseudo-ChE
in the plasma and decreases its susceptibility to
AChE, thereby increasing its potency and duration of
action compared to those of ACh.
Carbachol differs from ACh only in the substitution of a
carbamoyl group for the terminal methyl group of ACh.
This substitution makes carbachol completely resistant to
degradation by cholinesterases but does not improve its
selectivity for muscarinic versus nicotinic receptors.
Bethanechol combines the addition of the methyl group
and the substitution of the terminal carbamoyl group,
producing a drug that is a selective agonist of muscarinic
receptors and is resistant to degradation by cholinesterases.
Cholinomimetic drugs are useful for treating glaucoma because they
can decrease the resistance to the movement of fluid (aqueous humor)
out of the eye, thereby reducing the intraocular pressure.
Surgery of the Eye
Cataract surgery sometimes requires the use of acetylcholine to
constrict the pupil rapidly.
Postpartum and postoperative non obstructive urinary retention or
urinary retention caused by neurogenic bladder. ( Bethanicol )
Pilocarpine is administered orally in 5–10-mg doses given three times
daily for the treatment of xerostomia
Potentially severe adverse effects can result from
systemic administration of cholinomimetic drugs,and
none should be administered by intramuscular or
If significant amounts of these drugs enter the
Nausea , abdominal cramps, diarrhea, salivation,
hypotension with reflex tachycardia, cutaneous
vasodilation, sweating, and broncho constriction can
Inhibition of AChE potentiates and prolongs the stimulation
of cholinoreceptors resulting from ACh released at
These synapses found at the skeletal neuromuscular
junction, adrenal medulla, autonomic ganglia, and
cholinergic synapses in the CNS.
Inhibition of AChE can increase the stimulation of both
muscarinic and nicotinic receptors produced by synaptically
several AChE inhibitors also inhibit the pseudo-ChE in
plasma. This can permit plasma concentrations of ACh to
rise markedly and activate endothelial muscarinic receptors.
Action • Inhibits the breakdown of acetylcholine so that it
accumulates and has a prolonged effect. Result is generalized
cholinergic response, including : -
› Increased tone of intestinal and skeletal musculature.
› Bronchial and ureteral constriction.
› Increased salivation.
› CNS stimulation.
Absorption: Readily absorbed from
subcut and IM sites.
Distribution: Widely distributed;
crosses the blood-brain barrier.
Half-life: 1–2 hours.