C H A P T E R 3 3
Anticholinergic agents
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pregnancy
because of the potential for adverse effects
to the fetus
; hypertension
because of the possibility
of additive hypertensive effects from the sympathetic
system’s dominance with parasympathetic nervous
system blocking
; and spasticity and brain damage,
which could be exacerbated by cholinergic blockade
within the CNS.
Adverse effects
The adverse effects associated with the use of antichol
inergic drugs are caused by the systemic blockade of
cholinergic receptors. What are adverse effects in some
cases may be the desired therapeutic effects in others
(Table 33.2). The intensity of adverse effects is related
to drug dose: the more of the drug in the system, the
greater are the systemic effects. These adverse effects
could include CNS effects, such as blurred vision, pupil
dilation and resultant photophobia, cycloplegia and
increased intraocular pressure, all of which are related
to the blocking of the parasympathetic effects in the eye.
Weakness, dizziness, insomnia, mental confusion
and excitement are effects related to cholinergic receptor
blockade within the CNS. Dry mouth results from the
blocking of GI secretions. Altered taste perception,
nausea, heartburn, constipation, bloated feelings and
paralytic ileus are related to a slowing of GI activity.
Tachycardia and palpitations are possible effects related
to blocking of the parasympathetic effects on the heart.
Urinary hesitancy and retention are related to the
blocking of bladder muscle activity and sphincter relaxa-
tion. Decreased sweating and an increased predisposition
to heat prostration are related to the inability to cool the
body by sweating, a result of blocking of the sympathetic
cholinergic receptors responsible for sweating. Suppres-
sion of breastfeeding is related to anticholinergic effects
in the breasts and in the CNS. The severity of the adverse
effects is related to the dose of the drug.
Clinically important drug–drug interactions
The incidence of anticholinergic effects increases if
these drugs are combined with any other drugs with
anticholinergic activity, including antihistamines,
antiparkinsonism drugs, monoamine oxidase (MAO)
inhibitors and tricyclic antidepressants (TCAs). If
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TABLE 33.2 Effects of parasympathetic blockade and associated therapeutic uses
Physiological effect
Therapeutic uses
Gastrointestinal
Smooth muscle: blocks spasm, blocks peristalsis
Secretory glands: decreases acid and digestive enzyme
production
Decreases motility and secretory activity in peptic ulcer,
gastritis, cardiospasm, pylorospasm, enteritis, diarrhoea,
hypertonic constipation
Urinary tract
Decreases tone and motility in the ureters and fundus of
the bladder; increases tone in the bladder sphincter
Increases bladder capacity in children with enuresis,
spastic paraplegics; decreases urinary urgency and
frequency in cystitis; antispasmodic in renal colic and to
counteract bladder spasm caused by morphine
Biliary tract
Relaxes smooth muscle, antispasmodic
Relief of biliary colic; counteracts spasms caused by narcotics
Bronchial muscle
Weakly relaxes smooth muscle
Aerosol form may be used in asthma; may counteract
bronchoconstriction caused by drugs
Cardiovascular system
Increases heart rate (may decrease heart rate at very low
doses); causes local vasodilation and flushing
Counteracts bradycardia caused by vagal stimulation,
carotid sinus syndrome, surgical procedures; used to
overcome heart blocks following MI; used to counteract
hypotension caused by cholinergic drugs
Ocular effects
Pupil dilation, cycloplegia
Allows ophthalmological examination of the retina, optic
disc; relaxes ocular muscles and decreases irritation in
iridocyclitis, choroiditis
Secretions
Reduces sweating, salivation, respiratory tract secretions
Preoperatively before inhalation anaesthesia; reduces
nasal secretions in rhinitis, hay fever; may be used to
reduce excessive sweating in hyperhidrosis
Central nervous system
Decreases extrapyramidal motor activity
Atropine may cause excessive stimulation, psychosis,
delirium, disorientation
Decreases tremor in parkinsonism; helps to prevent
motion sickness
