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Chapter 20
Cholinergic Drugs
Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Drugs that stimulate the parasympathetic nervous system (PSNS) The PSNS is the opposing system to
the sympathetic nervous system (SNS)
Cholinergic Drugs
2Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Also known as cholinergic agonists or parasympathomimetics
Mimic effects of the PSNS neurotransmitter acetylcholine (ACh)
Cholinergic Drugs (cont’d)
3Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
4Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Two types, determined by: Location Action once stimulated
Nicotinic receptors Muscarinic receptors
Cholinergic Receptors
5Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Located in the ganglia of both the PSNS and SNS
Named nicotinic because they can be stimulated by the alkaloid nicotine
Nicotinic Receptors
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Located postsynaptically in the effector organs of the PSNS Smooth muscle Cardiac muscle Glands
Named muscarinic because they can be stimulated by the alkaloid muscarine
Muscarinic Receptors
7Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
8Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Direct-acting cholinergic agonists Bind to cholinergic receptors, activating them
Indirect-acting cholinergic agonists Inhibit the enzyme acetylcholinesterase, which breaks
down ACh Results in more ACh available at the receptors
Cholinergic Drugs: Mechanism of Action
9Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
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 to break these bonds
Indirect-Acting (Cholinesterase Inhibitors)
10Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Effects seen when PSNS is stimulated The PSNS is the “rest and digest” system
Drug Effects
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Stimulate intestine and bladder Increased gastric secretions Increased gastrointestinal motility Increased urinary frequency
Stimulate pupils Constriction (miosis) Reduced intraocular pressure
Increased salivation and sweating
Drug Effects (cont’d)
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Cardiovascular effects Decreased heart rate Vasodilation
Respiratory effects Bronchial constriction, narrowed airways
Cholinergic Drug Effects (cont’d)
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At recommended doses, cholinergics primarily affect muscarinic receptors
At high doses, cholinergics stimulate nicotinic receptors
Desired effects are from muscarinic receptor stimulation
Many undesirable effects are caused by stimulation of nicotinic receptors
Cholinergic Drug Effects (cont’d)
14Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Classroom Response QuestionThe nurse is assessing a patient who has been taking a cholinergic drug for 3 days. The patient has flushed skin, orthostatic blood pressure changes, and is complaining of abdominal cramps and nausea. The nurse recognizes that the patient is most likely experiencing
A.early signs of a cholinergic crisis.
B.late signs of a cholinergic crisis.
C.an allergic reaction to the drug.
D.expected adverse effects.
15Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Direct-acting drugs Reduce intraocular pressure Useful for glaucoma and intraocular surgery
• echothiophate
• carbachol
• pilocarpine
Topical application because of poor oral absorption
Indications
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Direct-acting drug—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 subcutaneous injection
Indications (cont’d)
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Indirect-acting drugs Cause skeletal muscle contractions Used for diagnosis and treatment of
myasthenia gravis Used to reverse neuromuscular blocking drugs Used to reverse anticholinergic poisoning (antidote)
• Examples: physostigmine, pyridostigmine
Indications (cont’d)
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Indirect-acting anticholinesterase drugs Used for treatment of mild to moderate Alzheimer’s
disease• donepezil (Aricept)
• galantamine (Razadyne)
• rivastigmine (Exelon)
Indications (cont’d)
19Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
memantine (Namenda) Not a cholinergic drug Also used in the treatment of Alzheimer’s disease
Indications (cont’d)
20Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Adverse effects are a result of overstimulation of the PSNS
Cardiovascular Bradycardia, hypotension, syncope, conduction
abnormalities (AV block and cardiac arrest) CNS
Headache, dizziness, convulsions, ataxia Gastrointestinal
Abdominal cramps, increased secretions, nausea, vomiting
Adverse Effects
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Respiratory Increased bronchial secretions, bronchospasms
Other Lacrimation, sweating, salivation, miosis
Adverse Effects (cont’d)
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Anticholinergics, antihistamines, sympathomimetics Antagonize cholinergic drugs, resulting in decreased
responses Other cholinergic drugs
Additive effects
Interactions
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Common uses Prevent memory loss Vertigo Tinnitus
May cause GI upset, headache, bleeding Potential interactions
Aspirin NSAIDs Anticoagulants Anticonvulsants
Herbal Products: Gingko
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Classroom Response QuestionA 60-year-old woman asks the nurse about taking ginkgo to help with her memory. The patient has a history of arthritis, type 2 diabetes, thyroid disease, and hypertension. She is currently taking NSAIDs for arthritis, oral antidiabetic medications, thyroid replacement hormone, and a beta blocker for blood pressure. What potential adverse effect from the gingko would be of most concern for this patient?
A.Stomach upset
B.Diarrhea
C.Bleeding
D.Drowsiness25Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Note that these drugs 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 vital signs and systems overview
Nursing Implications
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Medications should be taken as ordered and not abruptly stopped
Doses should be spread evenly apart to optimize the effects of the medication
Overdosing can cause life-threatening problems. Patients should not adjust dosages unless directed by their health care provider
Nursing Implications (cont’d)
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Classroom Response Question
A patient is scheduled to have lunch at 1200. The nurse will administer the pyridostigmine (Mestinon) at what time for optimal therapeutic effect?
A.1100
B.1130
C.1200
D.1230
28Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Encourage patients with myasthenia gravis to take medication 30 minutes before eating to help improve chewing and swallowing
When cholinergic drugs are prescribed for Alzheimer’s disease, be honest with caregivers and patients that the drugs are for management of symptoms (not a cure)
Therapeutic effects of anti-Alzheimer’s drugs may not occur for up to 6 weeks
Nursing Implications (cont’d)
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Classroom Response Question
A patient with Alzheimer’s disease accidentally took 2 weeks’ worth of a cholinergic medication. He is brought to the emergency department, is going into shock, and experiencing severe hypotension and vomiting. The nurse will expect which initial treatment?
A.Administration of physostigmine
B.Administration of atropine
C.Administration of epinephrine
D.Cardiovascular support with dopamine
30Copyright © 2014 by Mosby, an imprint of Elsevier Inc.
Atropine is the antidote for cholinergics, and 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
Nursing Implications (cont’d)
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Monitor for therapeutic effects Alleviated signs and symptoms of myasthenia gravis In postoperative patients with decreased GI
peristalsis, monitor for: • Increased bowel sounds
• Passage of flatus
• Occurrence of bowel movements
Nursing Implications (cont’d)
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Monitor for therapeutic effects In patients with urinary retention/hypotonic bladder,
urination should occur within 60 minutes of bethanechol administration
In patients with Alzheimer’s disease:• Improvement in symptoms
• Improvement in mood and decrease in confusion
Monitor for adverse effects
Nursing Implications (cont’d)
33Copyright © 2014 by Mosby, an imprint of Elsevier Inc.