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Cholinergic Agents and Cholinergic Blocking-Agents

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					Drugs Affecting the Autonomic Nervous System
Cholinergic Agents and Cholinergic Blocking Agents

Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved.

Cholinergic Agents
• Drugs that stimulate the parasympathetic nervous system (PSNS) • The PSNS is the opposing system to the SNS

Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved.

Cholinergic Agents
Also known as • cholinergic agonists

or
• parasympathomimetics

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Instructors may wish to use EIC Image #56: The Parasympathetic and Sympathetic Nervous Systems and Their Relationships to One Another

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Cholinergic Agents
• Mimic the effects of the PSNS neurotransmitter • Acetylcholine (ACh)

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Cholinergic Receptors
Two types, determined by:
• Location

• Action once stimulated

Nicotinic receptors and Muscarinic receptors

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Nicotinic Receptors
• Located in the ganglia of both the PSNS and SNS • Named ―nicotinic‖ because can be stimulated by the alkaloid nicotine

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Muscarinic Receptors
• Located postsynaptically:
– Smooth muscle

– Cardiac muscle – Glands of parasympathetic fibers – Effector organs of cholinergic sympathetic fibers

• Named ―muscarinic‖ because can be stimulated by the alkaloid muscarine
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Instructors may wish to insert EIC Image #57:

The Sympathetic, Parasympathetic, and Somatic Nervous Systems
This slide illustrates location of the nicotinic and muscarinic receptors within the PSNS.

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Lisa L. HHS: Hernandez: HHS: Is there copy missing at the end? Inhibiting what?

Adrenergic Agents: Mechanism of Action
• Direct-acting (agonist)
– Bind to cholinergic receptors, causing stimulation

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Adrenergic Agents: Mechanism of Action
• Indirect-acting
– Inhibit the enzyme ―cholinesterase‖ Result: more ACh is available at the receptors

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Indirect-Acting Cholinergic Agents (Cholinesterase Inhibitors)
• Reversible
– Bind to cholinesterase for a period of minutes to hours

• Irreversible
– Bind to cholinesterase and form a permanent covalent bond – The body must make new cholinesterase

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Drug Effects of Cholinergic Agents
• Effects seen when the PSNS is stimulated. • The PSNS is the ―rest and digest‖ system.

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Drug Effects of Cholinergic Agents
―SLUDGE‖ • Salivation • Lacrimation • Urinary incontinence • Diarrhea • Gastrointestinal cramps
• Emesis
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Drug Effects of Cholinergic Agents
• Stimulate intestine and bladder
– Increased gastric secretions – Increased gastrointestinal motility – Increased urinary frequency

• Stimulate pupil
– Constriction (miosis) – Reduced intraocular pressure

• Increased salivation and sweating
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Drug Effects of Cholinergic Agents
• Cardiovascular effects
– Decreased heart rate

– Vasodilation

• Respiratory effects
– Bronchial constriction, narrowed airways

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Drug Effects of Cholinergic Agents
• At recommended doses, the cholinergics primarily affect the MUSCARINIC receptors. • At high doses, cholinergics stimulate the NICOTINIC receptors.

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Drug Effects of Cholinergic Agents
• DESIRED EFFECTS: from muscarinic receptor stimulation • Many undesirable effects are due to stimulation of the nicotinic receptors

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Cholinergic Agents: Therapeutic Uses
Direct-Acting Agents
• Reduce intraocular pressure

• Useful for glaucoma and intraocular surgery Examples: acetylcholine, carbachol, pilocarpine

Topical application due to poor oral absorption

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Cholinergic Agents: Therapeutic Uses
Direct-Acting Agent—bethanechol
• Increases tone and motility of bladder and GI tract

• Relaxes sphincters in bladder and GI tract, allowing them to empty • Helpful for postsurgical atony of the bladder and GI tract
Oral dose or SC injection

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Cholinergic Agents: Therapeutic Uses
Indirect-Acting Agents
• Cause skeletal muscle contractions

• Used for diagnosis and treatment of myasthenia gravis • Used to reverse neuromuscular blocking agents • Used to reverse anticholinergic poisoning (antidote) Examples: physostigmine, pyridostigmine

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Cholinergic Agents: Therapeutic Uses
Indirect-Acting Agent—donepezil (Aricept)
• Used in the treatment of mild to moderate Alzheimer’s disease. • Helps to increase or maintain memory and learning capabilities.

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Cholinergic Agents: Side Effects
Side effects are a result of overstimulation of the PSNS.
• Cardiovascular: – Bradycardia, hypotension, conduction abnormalities (AV block and cardiac arrest) • CNS: – Headache, dizziness, convulsions • Gastrointestinal: – Abdominal cramps, increased secretions, nausea, vomiting
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Cholinergic Agents: Side Effects
Side effects are a result of overstimulation of the PSNS.
• Respiratory:

– Increased bronchial secretions, bronchospasms • Other: – Lacrimation, sweating, salivation, loss of binocular accommodation, miosis

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Cholinergic Agents: Interactions
• Anticholinergics, antihistamines, sympathomimetics • Antagonize cholinergic agents, resulting in decreased responses

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Cholinergic Agents: Nursing Implications
• Keep in mind that these agents will stimulate the PSNS and mimic the action of ACh. • Assess for allergies, presence of GI or GU obstructions, asthma, peptic ulcer disease, or coronary artery disease.

• Perform baseline assessment of VS and systems overview.

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Cholinergic Agents: Nursing Implications
• Medications should be taken as ordered and not abruptly stopped. • The doses should be spread evenly apart to optimize the effects of the medication.

• Overdosing can cause life-threatening problems. Patients should not adjust the dosages unless directed by the physician.

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Cholinergic Agents: Nursing Implications
• Encourage patients with myasthenia gravis to take medication 30 minutes before eating to help improve chewing and swallowing.

• When donepezil is prescribed for Alzheimer’s disease, be honest with caregivers and patients that the drug is for management of symptoms, not for a cure. • Therapeutic effects of donepezil may not occur for up to 6 weeks.
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Cholinergic Agents: Nursing Implications
• Atropine is the antidote for cholinergics. It should be available in the patient’s room for immediate use if needed.

• Patients should notify their physician if they experience muscle weakness, abdominal cramps, diarrhea, or difficulty breathing.

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Cholinergic Agents: Nursing Implications
Monitor for side effects, including:
Increased respiratory secretions Bronchospasms Difficulty breathing Nausea and vomiting Abdominal cramping Dysrhythmias Hypotension Bradycardia

Diarrhea Increase in frequency and urgency of voiding patterns

Increased sweating

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Cholinergic Agents: Nursing Implications
Monitor for therapeutic effects:
• Alleviated signs and symptoms of myasthenia gravis
• In postoperative patients with decreased GI peristalsis, look for:

– Increased bowel sounds
– Passage of flatus – Occurrence of bowel movements • In patients with urinary retention/hypotonic bladder, urination should occur within 60 minutes of bethanecol administration
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Cholinergic Blocking Agents
• Drugs that block or inhibit the actions of acetylcholine (ACh) in the parasympathetic nervous system (PSNS)

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Cholinergic Blocking Agents: Mechanism of Action
• Competitive antagonists • Compete with ACh

• Block ACh at the muscarinic receptors in the PSNS
– As a result, ACh is unable to bind to the receptor site and cause a cholinergic effect.

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Cholinergic Blocking Agents: Mechanism of Action
• Once these drugs bind to receptors, they inhibit nerve transmission at these receptors.

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Instructors may wish to use EIC Image #58: Site of Action of Cholinergic Blockers Within the PSNS

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Cholinergic Blocking Agents: Chemical Class
Natural
atropine

Synthetic/Semisynthetic
anisotropine clidinium

belladonna hyoscyamine scopolamine

dicyclomine hexocyclium ipratropium
oxybutynin

glycopyrrolate homatropine isopropamide
propantheline

tolterodine
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tridihexethyl

Drug Effects of Cholinergic Blocking Agents
• Cardiovascular
– Small doses: decrease heart rate

– Large doses: increase heart rate

• CNS
– Small doses: decrease muscle rigidity and tremors – Large doses: drowsiness, disorientation, hallucinations
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Drug Effects of Cholinergic Blocking Agents
• Eye
– Dilated pupils (mydriasis)

– Decreased accommodation due to paralysis of ciliary muscles (cycloplegia)

• Gastrointestinal
– Relax smooth muscle tone of GI tract
– Decrease intestinal and gastric secretions

– Decrease motility and peristalsis
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Drug Effects of Cholinergic Blocking Agents
• Genitourinary
– Relaxed detrusor muscle – Increased constriction of internal sphincter – Result: urinary retention

• Glandular
– Decreased bronchial secretions, salivation, sweating

• Respiratory
– Decreased bronchial secretions – Dilated bronchial airways
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Cholinergic Blocking Agents: Therapeutic Uses
CNS
Decreased muscle rigidity and muscle tremors

• Parkinson’s disease
• Drug-induced extrapyramidal reactions

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Cholinergic Blocking Agents: Therapeutic Uses
Cardiovascular
Affect the heart’s conduction system
• Low doses: slow the heart rate • High doses: block inhibitory vagal effects on the SA and AV node pacemaker cells – Result: increased heart rate

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Cholinergic Blocking Agents: Therapeutic Uses
Atropine
Used primarily for cardiovascular disorders
• Sinus node dysfunction • Symptomatic second-degree heart block
• Sinus bradycardia with hemodynamic compromise (advanced life support)

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Cholinergic Blocking Agents: Therapeutic Uses
Respiratory
Blocking the cholinergic stimulation of the PSNS allows unopposed action of the SNS.
• Results: – Decreased secretions from nose, mouth, pharynx, bronchi

– Relaxed smooth muscles in bronchi and bronchioles – Decreased airway resistance – Bronchodilation
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Cholinergic Blocking Agents: Therapeutic Uses
Respiratory agents are used to treat:
• Exercise-induced bronchospasms

• Chronic bronchitis • Asthma • Chronic obstructive pulmonary disease

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Cholinergic Blocking Agents: Therapeutic Uses
Gastrointestinal
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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Cholinergic Blocking Agents: Therapeutic Uses
Gastrointestinal agents are used to treat:
• Peptic ulcer disease

• Irritable bowel disease • GI hypersecretory states

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Cholinergic Blocking Agents: Therapeutic Uses
Genitourinary
• Relaxed detrusor muscles of the bladder

• Increased constriction of the internal sphincter • Reflex neurogenic bladder • Incontinence

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Cholinergic Blocking Agents: Side Effects
Body System
Cardiovascular

Side/Adverse Effects
Increased heart rate, dysrhythmias

CNS

CNS excitation, restlessness, irritability, disorientation, hallucinations, delirium

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Cholinergic Blocking Agents: Side Effects
Body System
Eye

Side/Adverse Effects
Dilated pupils, decreased visual accommodation, increased intraocular pressure
Decreased salivation, decreased gastric secretions, decreased motility

Gastrointestinal

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Cholinergic Blocking Agents: Side Effects
Body System
Genitourinary

Side/Adverse Effects
Urinary retention

Glandular Respiratory

Decreased sweating Decreased bronchial secretions

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Cholinergic Blocking Agents: Interactions
• Antihistamines, phenothiazines, tricyclic antidepressants, MAOIs • When given with cholinergic blocking agents, cause ADDITIVE cholinergic effects, resulting in increased effects

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Cholinergic Blocking Agents: Nursing Implications
• Keep in mind that these agents will block the action of ACh in the PSNS. • Assess for allergies, presence of BPH, glaucoma, tachycardia, MI, CHF, hiatal hernia, and GI or GU obstruction.

• Perform baseline assessment of VS and systems overview.

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Cholinergic Blocking Agents: Nursing Implications
• Medications should be taken exactly as prescribed to have the maximum therapeutic effect.

• Overdosing can cause life-threatening problems.
• Blurred vision may cause problems with driving or operating machinery.

• Patients may experience sensitivity to light and may want to wear dark glasses or sunglasses.

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Cholinergic Blocking Agents: Nursing Implications
• When giving ophthalmic solutions, apply pressure to the inner canthus to prevent systemic absorption.

• Dry mouth may occur; can be handled by chewing gum, frequent mouth care, and hard candy.
• Check with physician before taking any other medication, including OTC medications. • ANTIDOTE for atropine is physostigmine salicylate (Antilirium).

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Cholinergic Blocking Agents: Nursing Implications
• Anticholinergics may lead to higher risk for heat stroke due to 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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Cholinergic Blocking Agents: Nursing Implications
• Patients should report the following to their physician: urinary hesitancy and/or retention, constipation, palpitations, tremors, confusion, sedation or amnesia, excessive dry mouth (especially if they have chronic lung infections or disease), or fever

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Cholinergic Agents: Nursing Implications
• Monitor for therapeutic effects: • For patients with Parkinson’s disease: fewer tremors and decreased salivation and drooling

• For patients with peptic ulcer disease: decreased abdominal pain

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Cholinergic Blocking Agents: Nursing Implications
Monitor for side effects, including:
Constipation Tachycardia

Tremors Hallucinations Urinary retention
Fever

Confusion Sedation Hot, dry skin

CNS depression (occurs with large doses of atropine)
Copyright © 2002, 1998, Elsevier Science (USA). All rights reserved.


				
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