506
P A R T 5
Drugs acting on the autonomic nervous system
such combinations must be used, the person should
be monitored closely and dose adjustments made.
People should be advised to avoid over-the-counter
products that contain these drugs. The effectiveness
of phenothiazines decreases if they are combined
with anticholinergic drugs and the risk of paralytic
ileus increases. This combination should be avoided.
Anticholinergics also may interact with certain herbal
therapies (see Box 33.2).
■■
At cholinergic receptor sites, anticholinergic drugs
block the effects of acetylcholine. Because they block
the effects of the parasympathetic nervous system,
they are also known as parasympatholytic drugs.
■■
When the parasympathetic system is blocked, the
pupils dilate, the heart rate rises, and GI activity and
urinary bladder tone and function decrease.
KEY POINTS
Safe medication administration
Atropine toxicity
Although atropine is used in a large variety of clinical settings
(see Table 33.1 for usual indications), this drug can also be a
poison, causing severe toxicity. Because it is found in many
natural products, including the belladonna plant, and may be
present in herbal or alternative therapy products, atropine
toxicity can occur inadvertently. Atropine toxicity should be
considered whenever a person receiving an anticholinergic
drug presents with a sudden onset of bizarre mental and
neurological symptoms. Toxicity is dose related and usually
progresses as follows:
0.5 mg atropine: slight cardiac slowing, dryness of mouth,
inhibition of sweating
1.0 mg atropine: definite mouth and throat dryness, thirst,
rapid heart rate, pupil dilation
2.0 mg atropine: rapid heart rate, palpitations; marked mouth
dryness; dilated pupils; some blurring of vision
5.0 mg atropine: all of the foregoing and marked speech
disturbances; difficulty swallowing; restlessness, fatigue
and headache; dry and hot skin; difficulty voiding; reduced
intestinal peristalsis
10.0 mg atropine: all of the foregoing symptoms, more
marked; pulse rapid and weak; iris nearly gone; vision
blurred; skin flushed, hot, dry and scarlet; ataxia;
restlessness and excitement; hallucinations; delirium
and coma
Treatment is as follows. If the poison was taken orally,
immediate gastric lavage should be done to limit absorption.
Physostigmine can be used as an antidote, however it is
controversial. It can result in serious adverse effects and
is only recommended in life threatening situations. A slow
intravenous injection of 0.5 to 4 mg (depending on the size
of the individual) usually reverses the delirium and coma of
atropine toxicity. Physostigmine is metabolised rapidly, so the
injection may need to be repeated every 1 to 2 hours until
the atropine has been cleared from the system. Diazepam
is the drug of choice if an anticonvulsant is needed. Cool
baths and alcohol sponging may relieve the fever and hot
skin. In extreme cases, respiratory support may be needed.
It is important to remember that the half-life of atropine is
2.5 hours; at extremely high doses, several hours may be
needed to clear the atropine from the body.
Prototype summary: Atropine
Indications:
To decrease secretions before surgery,
treatment of parkinsonism, restoration of
cardiac rate and arterial pressure following vagal
stimulation, relief of bradycardia and syncope
due to hyperactive carotid sinus reflex, relief of
pylorospasm, relaxation of the spasm of biliary and
ureteral colic and bronchospasm, control of crying
and laughing episodes associated with brain lesions,
relaxation of uterine hypertonicity, management of
peptic ulcer, control of rhinorrhoea associated with
hay fever, antidote for cholinergic overdose and
poisoning from various mushrooms.
Actions:
Competitively blocks acetylcholine
muscarinic receptor sites, blocking the effects of the
parasympathetic nervous system.
Pharmacokinetics:
Route Onset
Peak
Duration
IM 10–15 mins 30 mins
4 hours
IV Immediate 2–4 mins
4 hours
SC Varies
1–2 hours
4 hours
Topical 5–10 mins 30–40 mins 7–14 days
T
1/2
:
2.5 hours, with metabolism in the liver and
excretion in the urine.
Adverse effects:
Blurred vision, mydriasis,
cycloplegia, photophobia, palpitations, bradycardia,
dry mouth, altered taste perception, urinary
hesitancy and retention, decreased sweating and
predisposition to heat prostration (see Focus on safe
medication administration for more information
about atropine toxicity).
The risk of anticholinergic effects can be exacerbated
if anticholinergic agents are combined with burdock,
rosemary or turmeric used as herbal therapy. Advise
people who use herbal therapies to avoid these
combinations.
Herbal and alternative therapies
BOX 33.2
