1. Cholinergic-Blocking Drugs
Chapter 21
Cholinergic-Blocking Drugs
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2. Cholinergic-Blocking Drugs
Drugs that block or inhibit the actions of acetylcholine (ACh) in the parasympathetic nervous system (PSNS)
Also known as anticholinergics, parasympatholytics, and antimuscarinic drugs
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Mechanism of Action
Competitive antagonists
Compete with ACh for binding at muscarinic receptors in the PSNS
As a result, ACh is unable to bind to the receptor site and cause a cholinergic effect.
When these drugs bind to receptors, they inhibit nerve transmission at these receptors.
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Site of action of cholinergic blockers in the parasympathetic nervous system. ACh, Acetylcholine
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5. Cholinergic-Blocking Drugs: Examples
atropine
dicyclomine (Bentyl)
glycopyrrolate (Robinul)
oxybutynin (Ditropan)
scopolamine (Transderm-Scōp)
tolterodine (Detrol)
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Drug Effects
Cardiovascular
Small doses: decrease heart rate
Large doses: increase heart rate
Central nervous system (CNS)
Small doses: decrease muscle rigidity and tremors
Large doses: drowsiness, disorientation, hallucinations
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Drug Effects (Cont.)
Eye
Dilated pupils (mydriasis)
Decreased accommodation caused by paralysis of ciliary muscles (cycloplegia)
Gastrointestinal (GI)
Relax smooth muscle tone of GI tract
Decrease intestinal and gastric secretions
Decrease motility and peristalsis
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8. Audience Response System Question
Which finding would the nurse anticipate when assessing a patient with an atropine overdose?
Moist skin
Miosis
Bradycardia
Urinary retention
Correct answer: D
Rationale: Atropine overdose is manifested by flushing, dry skin and mucous membranes, mydriasis, altered mental status, and fever. Other serious effects include sinus tachycardia, urinary retention, hypertension, hallucinations, and cardiovascular collapse. Activated charcoal is usually given along with supportive therapy.
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Drug Effects (Cont.)
Genitourinary (GU)
Relaxed detrusor muscle
Increased constriction of internal sphincter
Result: urinary retention
Glandular
Decreased bronchial secretions, salivation, sweating
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Drug Effects (Cont.)
Respiratory
Decreased bronchial secretions
Dilated bronchial airways
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11. Indications: Central Nervous System
Decreasing muscle rigidity and muscle tremors
Parkinson’s disease
Drug-induced extrapyramidal reactions such as those associated with antipsychotic drugs
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12. Indications: Cardiovascular
Affects the heart’s conduction system
Low doses: slow the heart rate
High doses: block inhibitory vagal effects on sinoatrial and atrioventricular node pacemaker cells
Results in increased heart rate
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13. Indications: Cardiovascular (Cont.)
Atropine
Used primarily for cardiovascular disorders
Diagnosis of sinus node dysfunction
Symptomatic second-degree heart block
Severe sinus bradycardia with hemodynamic compromise (advanced life support)
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14. Indications: Respiratory
Blocking the cholinergic stimulation of the PSNS allows unopposed action of the SNS.
Results
Decreased secretions from the nose, mouth, pharynx, and bronchi
Relaxed smooth muscles in the bronchi and bronchioles
Decreased airway resistance
Bronchodilation
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15. Indications: Respiratory (Cont.)
Cholinergic blockers are used to treat:
Exercise-induced bronchospasms
Chronic bronchitis
Asthma
Chronic obstructive pulmonary disease
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16. Indications: Gastrointestinal
The PSNS controls gastric secretions and smooth muscles that produce gastric motility.
Blockade of PSNS results in:
Decreased secretions
Relaxation of smooth muscle
Decreased GI motility and peristalsis
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17. Indications: Gastrointestinal (Cont.)
GI drugs are used to treat:
Irritable bowel disease
GI hypersecretory states
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18. Indications: Genitourinary
Reflex neurogenic bladder
Incontinence
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19. Audience Response System Question
Glycopyrrolate (Robinul) and an opioid are administered to a patient before surgery in the preoperative area. The anticholinergic is used to
potentiate the action of the opioid.
assist the patient in retaining urine during surgery.
control secretions during surgery.
prevent nausea.
Correct answer: C
Rationale: Anticholinergics such as glycopyrrolate and atropine are given preoperatively to reduce or control secretions before and during surgery.
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Contraindications
Known drug allergy
Angle-closure glaucoma
Acute asthma or other respiratory distress
Myasthenia gravis
Acute cardiovascular instability
GI or GU tract obstruction (e.g., benign prostatic hyperplasia [BPH])
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Adverse Effects
Body System
Adverse Effects
Cardiovascular CNS
Increased heart rate, dysrhythmias CNS excitation, restlessness, irritability, disorientation, hallucinations, delirium
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22. Adverse Effects (Cont.)
Body System
Adverse Effects
Eye GI
Dilated pupils (causing blurred vision), increased intraocular pressure Decreased salivation, decreased gastric secretions, decreased motility (causing constipation)
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23. Adverse Effects (Cont.)
Body System
Adverse Effects
GU Glandular Respiratory
Urinary retention Decreased sweating Decreased bronchial secretions
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24. Audience Response System Question
Before administering tolterodine (Detrol), it is most important for the nurse to assess the patient for a history of which condition?
Angle-closure glaucoma
Cataracts
Hypothyroidism
Hyponatremia
Correct answer: A
Rationale: Tolterodine (Detrol) may worsen preexisting angle-closure glaucoma and urinary retention, so its use should be avoided in patients with these conditions.
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Toxicity and Overdose
Symptomatic and supportive therapy
Continuous electrocardiographic monitoring
Activated charcoal
Treatment of shock
Physostigmine
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Interactions
Amantadine, antihistamines, phenothiazines, tricyclic antidepressants, digoxin
When given with other cholinergic blocking drugs, cause additive cholinergic effects, resulting in increased effects
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Atropine
Naturally occurring antimuscarinic
Uses: bradycardia, ventricular asystole, antidote for anticholinesterase inhibitor toxicity or poisoning, and preoperatively to reduce salivation and GI secretions
Contraindications: angle-closure glaucoma, advanced hepatic and renal dysfunction, hiatal hernia associated with reflux esophagitis, intestinal atony, obstructive GI or GU conditions, and severe ulcerative colitis
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Bentyl
Synthetic antispasmodic cholinergic blocker
Uses: functional disturbances of GI motility such as irritable bowel syndrome.
Contraindications: known hypersensitivity to anticholinergics, angle-closure glaucoma, GI tract obstruction, myasthenia gravis, paralytic ileus, GI atony, and toxic megacolon
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Rubinol
Synthetic antimuscarinic drug
Blocks receptor sites in the autonomic nervous system that control the production of secretions
Use: preoperatively to reduce salivation and excessive secretions in the respiratory and GI tracts
Contraindications: hypersensitivity, angle-closure glaucoma, myasthenia gravis, GI or GU tract obstruction, tachycardia, myocardial ischemia, hepatic disease, ulcerative colitis, and toxic megacolon
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30. Oxybutynin (Ditropan)
Synthetic antimuscarinic drug
Uses: overactive bladder and antispasmodic for neurogenic bladder associated with spinal cord injuries and congenital conditions such as spina bifida
Contraindications: drug allergy, urinary or gastric retention, and uncontrolled angle-closure glaucoma
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Scopolamine
Naturally occurring cholinergic blocker and one of the principal belladonna alkaloids
Uses: prevention of motion sickness and to help prevent postoperative, postanesthesia nausea and vomiting
Contraindications: angle-closure glaucoma, advanced hepatic and renal dysfunction, hiatal hernia associated with reflux esophagitis, intestinal atony, obstructive GI or GU conditions, and severe ulcerative colitis
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Scopolamine (Cont.)
Adverse effects: drowsiness, dry mouth, and blurred vision
Using scopolamine with CNS depressants or alcohol may increase sedation.
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Tolterodine (Detrol)
Muscarinic receptor blocker
Uses: urinary frequency, urgency, and urge incontinence caused by bladder (detrusor) overactivity
Newer drugs for this purpose include solifenacin (Vesicare), darifenacin (Enablex), trospium (Sanctura), and fesoterodine (Toviaz).
Newer drugs are associated with a much lower incidence of dry mouth, partly because of their pharmacologic specificity for the bladder as opposed to the salivary glands.
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Mirabegron
Used to treat overactive bladder
Beta3 agonist; represents a new class of therapy for this condition
Does not have same side effects as other drugs to treat overactive bladder
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Nursing Implications
Keep in mind that these drugs block the action of ACh in the PSNS.
Assess for allergies, presence of BPH, urinary retention, glaucoma, tachycardia, myocardial infarction, heart failure, hiatal hernia, and GI or GU obstruction.
Perform baseline assessment of vital signs and systems overview.
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36. Nursing Implications (Cont.)
Medications should be taken exactly as prescribed to have the maximum therapeutic effect.
Overdosing can cause life-threatening problems.
Blurred vision will cause problems with driving or operating machinery.
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37. Nursing Implications (Cont.)
Patients may experience sensitivity to light and may want to wear dark glasses or sunglasses.
When giving ophthalmic solutions, apply pressure to the inner canthus to prevent systemic absorption.
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38. Nursing Implications (Cont.)
Dry mouth may occur; can be handled by chewing gum, frequent mouth care, and hard candy.
Patients should check with the physician before taking any other medication, including over-the-counter medications.
Antidote for atropine overdose is physostigmine.
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39. Nursing Implications (Cont.)
Anticholinergics taken by older adult patients may lead to higher risk for heatstroke because of the effects on heat-regulating mechanisms.
Teach patients to limit physical exertion and avoid high temperatures and strenuous exercise.
Emphasize the importance of adequate fluid and salt intake.
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40. Nursing Implications (Cont.)
Patients should report the following symptoms to their physician: urinary hesitancy or retention, constipation, tachycardia, palpitations, tremors, confusion, sedation, hallucinations, and decreased sweating (leading to hot, dry skin).
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41. Nursing Implications (Cont.)
Monitor for therapeutic effects.
For patients with Parkinson’s disease: fewer tremors and decreased salivation and drooling
For patients with urologic problems: improved urinary patterns, less hypermotility, increased time between voiding
Monitor for adverse effects.
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