McKenna's Pharmacology for Nursing, 2e

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P A R T 5  Drugs acting on the autonomic nervous system

lens accommodation Pupil dilation lacrimal secretions and salivation synaptate effect Effects of anticholinergic drugs

Pharmacodynamics of anticholinergic drugs

1 2

Acetyl CoA + Choline (from diet)

Nerve terminal

3

4

Enzyme

secretions heart rate contractility conduction

ACh

ACh

GI secretions motility sphincter constriction Muscle relaxation Sphincter constriction

Ca +

Ca +

Acetylcholinesterase

Cholinergic receptor

Anticholinergic drugs block the receptor site here

Neuron or effector cell

Vasoconstriction

Neuromuscular junction; causes muscle contraction

5 Oculomotor n. Facial n. Glossopharygeal n.

2 3 1

Vagus n. Pelvic n. 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.

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 ;

tachycardia and increased contractility that occurs when the parasympathetic nervous system is blocked ; impaired liver or kidney function, which could alter the