504
P A R T 5
Drugs acting on the autonomic nervous system
tachycardia and increased contractility that occurs
when the parasympathetic nervous system is blocked
;
impaired liver or kidney function,
which could alter the
metabolism and excretion of the drug
; and myasthenia
gravis,
which could worsen with further blocking of the
cholinergic receptors.
(Low doses of atropine are some-
times used in myasthenia gravis to block unwanted GI
and cardiovascular effects of the cholinergic drugs used
to treat that condition.)
Caution should be used in women who are breast-
feeding
because of possible suppression of breastfeeding
;
lens accommodation
Pupil dilation
lacrimal secretions
and salivation
synaptate effect
Effects of anticholinergic drugs
Pharmacodynamics of
anticholinergic drugs
ACh
ACh
Acetylcholinesterase
Acetyl CoA + Choline (from diet)
Enzyme
Cholinergic
receptor
Nerve
terminal
Neuron or
effector cell
Neuromuscular junction;
causes muscle contraction
Ca
+
Ca
+
Anticholinergic
drugs block
the receptor
site here
secretions
heart rate
contractility
conduction
GI secretions
motility
Muscle
relaxation
Sphincter
constriction
Vasoconstriction
sphincter
constriction
5
Oculomotor n.
Facial n.
Glossopharygeal n.
Vagus n.
Pelvic n.
1
2
2
3
3
4
1
4
5
FIGURE 33.1
Pharmacodynamics of anticholinergic drugs and associated physiological responses.
Safe medication administration
Applying dermal patch delivery systems
If a drug has been ordered to be given via a transdermal patch,
review the proper technique for applying a transdermal patch.
The patch should be applied to a clean, dry, intact and hairless
area of the body. Do not shave an area of application—that
could abrade the skin and lead to increased absorption. Hair
may be clipped if necessary. Peel off the backing without
touching the adhesive side of the patch (Figure 33.2). Place
the patch at a new site each time to avoid skin irritation or
degradation. Be sure to remove the old patch and clean the
area when putting on a new transdermal patch. It is important
to remember that many transdermal systems contain an
aluminised barrier that could cause an electrical charge with
arcing, smoke and severe transdermal burns if a defibrillator
is discharged over it or if the person has magnetic resonance
imaging (MRI). Remove any transdermal patches in the area if
a defibrillator is to be used or before the person has an MRI.
FIGURE 33.2
Carefully remove the backing from the patch without
touching the adhesive.
