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P A R T 5
Drugs acting on the autonomic nervous system
α-SPECIFIC ADRENERGIC AGONISTS
a
-specific adrenergic agonists (Table 30.2), or
a
-agonists, are drugs that bind primarily to
α
-receptors
rather than to
β
-receptors. Drugs belonging to this class
include clonidine (
Catapres
) and phenylephrine (
Abalon
,
Neo-Synephrine
).
Therapeutic actions and indications
Therapeutic effects of the
α
-specific adrenergic agonists
result from the stimulation of
α
-receptors within the
SNS (see Figure 30.2). The uses are varied, depending
on the specific drug and the route of administration
(Table 30.2).
Phenylephrine, a potent vasoconstrictor and
a
1
-agonist with little or no effect on the heart or bronchi,
is used in many combination cold and allergy products.
Parenterally it is used to treat shock or shock-like states,
to overcome paroxysmal supraventricular tachycardia,
to prolong local anaesthesia and to maintain blood
pressure during spinal anaesthesia. Topically it is used to
treat allergic rhinitis and to relieve the symptoms of otitis
media. Ophthalmically it is used to dilate the pupils for
eye examination, before surgery or to relieve elevated
eye pressure associated with glaucoma. Phenylephrine is
found in many cold and allergy products because it is
so effective in constricting topical vessels and decreasing
the swelling, signs and symptoms of rhinitis.
Clonidine specifically stimulates central nervous
system (CNS)
a
2
-receptors. This leads to decreased symp
athetic outflow from the CNS because the
a
2
-receptors
moderate the release of noradrenaline from the nerve
axon. Clonidine is available in oral and transdermal
Skin: colour and temperature
GI: abdominal examination
GU: urine output, bladder percussion and prostate
palpation
Respiratory: respiratory rate and adventitious sounds
Implementation
Ensure safe and appropriate administration of the drug.
Provide comfort and safety measures: temperature
and lighting control (person may have pupil dilation
secondary to sympathetic effects), mouth care and skin
care.
Monitor blood pressure, pulse rate and respiratory status
throughout drug therapy.
Provide support and reassurance to deal with drug therapy
and effects.
Provide teaching about drug name, dosage, side effects,
precautions and warning signs to report.
Evaluation
Evaluate drug effects: relief of enuresis.
Monitor for adverse effects: CV effects, dizziness, confusion,
headache, rash, difficulty voiding, sweating, flushing and
pupillary dilation.
Monitor for drug–drug interactions as indicated.
Evaluate the effectiveness of the teaching program as well
as comfort and safety measures.
TEACHING FOR M.C.
• The drug that you have been taking is ephedrine. It is
called an adrenergic agonist (or a sympathomimetic
drug). Ephedrine acts by mimicking the effects of the
sympathetic nervous system, which is the part of your
nervous system that is responsible for your response to
fear or danger (this is called the “fight-or-flight” response).
Because this drug triggers many effects in the body,
you may experience some undesired adverse effects.
It is crucial to discuss the effect of the drug with your
healthcare provider and to try to make the effect as
tolerable as possible.
• If the drug is in a solution, check it before each use. If the
solution is pink, brown or black, discard it.
• If you have diagnosed prostate problems, it might help to
void before taking each dose of the drug.
• Some of the following adverse effects may occur:
•
Restlessness or shaking
: If these occur, avoid driving,
operating machinery or performing delicate tasks.
•
Flushing or sweating
: Avoid warm temperatures and
heavy clothing; frequent washing with cool water may
help.
•
Heart palpitations
: If you feel that your heart is beating
too fast or skipping beats, sit down for a while and rest.
If the feeling becomes too uncomfortable, notify your
healthcare provider.
•
Sensitivity to light
: Avoid glaring lights or wear sunglasses
if you are in bright light. Be careful when moving
between extremes of light because your vision may not
adjust quickly.
• Report any of the following to your healthcare provider:
difficulty voiding, chest pain, difficulty breathing, dizziness,
headache or changes in vision.
• Do not stop taking this drug suddenly; make sure that you
have enough of your prescription. This drug dose should
be reduced gradually over 2 to 4 days when you are
instructed to discontinue it by your healthcare provider.
• Avoid OTC medications, including cold and allergy
remedies and diet pills. If you feel that you need one of
these, check with your healthcare provider first.
• Tell any healthcare provider who takes care of you that
you are taking this drug.
• Keep this drug and all medications out of the reach of
children. Do not share this drug with other people.
