502
P A R T 5
Drugs acting on the autonomic nervous system
(
Atrovent
),
propantheline (
Pro-Banthine
), and tiotro-
pium (
Spiriva
) (see Table 33.1).
Therapeutic actions and indications
The anticholinergic drugs competitively block the acetyl-
choline receptors at the muscarinic cholinergic receptor
sites that are responsible for mediating the effects of the
parasympathetic postganglionic impulses (Figure 33.1).
Some are more specific to particular receptors in the res-
piratory, genitourinary (GU) or GI tracts, making them
preferred for treating specific conditions, and others
more generally depress the parasympathetic system.
When the parasympathetic system is blocked, the effects
of the sympathetic system are more prominently seen.
These drugs can be used to decrease secretions before
anaesthesia; to treat parkinsonism (by blocking the
stimulating effects of acetylcholine); to restore cardiac
rate and blood pressure after vagal stimulation during
surgery; to relieve bradycardia caused by a hyperactive
carotid sinus reflex; to relieve pylorospasm and hyper-
active bowel; to relax biliary and ureteral colic; to relax
bladder detrusor muscles and tighten sphincters; to help
to control crying or laughing episodes in people with
brain injuries; to relax uterine hypertonicity; to help in
the management of peptic ulcer; to control rhinorrhoea
associated with hay fever; as an antidote for choliner-
gic drugs and for poisoning by certain mushrooms; and
as an ophthalmic agent to cause mydriasis or cyclo-
plegia in acute inflammatory conditions (Table 33.1).
Anticholinergic drugs also are thought to block the
effects of acetylcholine in the central nervous system
(CNS), which may account for their effectiveness in
treating motion sickness.
Atropine, the prototype drug, has been used for
many years and is derived from the plant
belladonna
.
(Belladonna was once used by fashionable ladies of the
European courts to dilate their pupils in an effort to make
them more innocent looking and alluring.) Atropine is
used to depress salivation and bronchial secretions and
to dilate the bronchi, but it can thicken respiratory secre-
tions (causing obstruction of airways). Atropine is also
used to inhibit vagal responses in the heart, to relax
the GI and GU tracts, to inhibit GI secretions, to cause
mydriasis
or relaxation of the pupil of the eye (also called
a mydriatic effect) and to cause
cycloplegia
, or inhibition
of the ability of the lens in the eye to accommodate to
near vision (also called a cycloplegic effect).
Atropine works by blocking only the muscarinic
effectors in the parasympathetic nervous system and
the few cholinergic receptors in the sympathetic nervous
system (SNS), such as those that control sweating. It acts
by competing with acetylcholine for the muscarinic ace-
tylcholine receptor sites. It does not block the nicotinic
receptors and therefore has little or no effect at the neu-
romuscular junction.
Ipratropium and tiotropium act more specifically to
decrease respiratory secretions and cause bronchodila-
tion. They are used as bronchodilators and to decrease
symptoms of upper respiratory irritation. These agents
BOX 33.1
Drug therapy across the lifespan
Anticholinergic agents/parasympatholytics
CHILDREN
The anticholinergic agents are often used in children.
Children are often more sensitive to the adverse effects of
the drugs, including constipation, urinary retention, heat
intolerance and confusion. If a child is given one of these
drugs, the child should be closely watched and monitored
for adverse effects, and appropriate supportive measures
should be instituted.
ADULTS
Adults need to be made aware of the potential for adverse
effects associated with the use of these drugs.They should
be encouraged to void before taking the medication if
urinary retention or hesitancy is a problem.They should
be encouraged to drink plenty of fluids and to avoid hot
temperatures because heat intolerance can occur and it will
be important to maintain hydration should this happen.
Safety precautions may be needed if blurred vision and
dizziness occur.The person should be urged not to drive or
perform tasks that require concentration and coordination.
PREGNANCY AND BREASTFEEDING
These drugs should not be used during pregnancy
because they cross the placenta and could cause adverse
effects on the fetus. If the benefit to the mother clearly
outweighs the potential risk to the fetus, they should be
used with caution. Breastfeeding women should find
another method of feeding the baby if an anticholinergic
drug is needed because of the potential for serious
adverse effects on the baby.
OLDER ADULTS
Older adults are more likely to experience the adverse
effects associated with these drugs; dose should be
reduced, and the person should be monitored very
closely. Because older people are more susceptible to
heat intolerance owing to decreased body fluid and
decreased sweating, extreme caution should be used
when an anticholinergic drug is given.The person should
be urged to drink plenty of fluids and to avoid extremes of
temperature or exertion in warm temperatures.The older
adult is more likely to experience confusion, hallucinations
and psychotic syndromes when taking an anticholinergic
drug. Safety precautions may be needed if central nervous
system effects are severe. Older adults may also have
renal impairment, making them more likely to have
problems excreting these drugs. Further reduction in dose
may be needed in the older person who also has renal
dysfunction.
