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Chapter 20
Cholinergic Drugs
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Cholinergic Drugs
Drugs that stimulate the parasympathetic nervous system (PSNS)
The PSNS is the opposing system to the sympathetic nervous system (SNS)
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3. Cholinergic Drugs (cont’d)
Also known as cholinergic agonists or parasympathomimetics
Mimic effects of the PSNS neurotransmitter acetylcholine (ACh)
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5. Cholinergic Receptors
Two types, determined by:
Location
Action once stimulated
Nicotinic receptors
Muscarinic receptors
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Nicotinic Receptors
Located in the ganglia of both the PSNS and SNS
Named nicotinic because they can be stimulated by the alkaloid nicotine
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Muscarinic Receptors
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
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9. Cholinergic Drugs: Mechanism of Action
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
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10. Indirect-Acting (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 to break these bonds
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Drug Effects
Effects seen when PSNS is stimulated
The PSNS is the “rest and digest” system
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Drug Effects (cont’d)
Stimulate intestine and bladder
Increased gastric secretions
Increased gastrointestinal motility
Increased urinary frequency
Stimulate pupils
Constriction (miosis)
Reduced intraocular pressure
Increased salivation and sweating
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13. Cholinergic Drug Effects (cont’d)
Cardiovascular effects
Decreased heart rate
Vasodilation
Respiratory effects
Bronchial constriction, narrowed airways
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14. Cholinergic Drug Effects (cont’d)
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
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15. Classroom Response Question
The 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
early signs of a cholinergic crisis.
late signs of a cholinergic crisis.
an allergic reaction to the drug.
expected adverse effects.
Correct answer: A
Rationale: The items listed are early signs of a cholinergic crisis, which can become more severe and lead to hypotension, circulatory collapse, bloody diarrhea, shock, and cardiac arrest.
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Indications
Direct-acting drugs
Reduce intraocular pressure
Useful for glaucoma and intraocular surgery
echothiophate
carbachol
pilocarpine
Topical application because of poor oral absorption
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Indications (cont’d)
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
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Indications (cont’d)
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
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Indications (cont’d)
Indirect-acting anticholinesterase drugs
Used for treatment of mild to moderate Alzheimer’s disease
donepezil (Aricept)
galantamine (Razadyne)
rivastigmine (Exelon)
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Indications (cont’d)
memantine (Namenda)
Not a cholinergic drug
Also used in the treatment of Alzheimer’s disease
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Adverse Effects
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
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22. Adverse Effects (cont’d)
Respiratory
Increased bronchial secretions, bronchospasms
Other
Lacrimation, sweating, salivation, miosis
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Interactions
Anticholinergics, antihistamines, sympathomimetics
Antagonize cholinergic drugs, resulting in decreased responses
Other cholinergic drugs
Additive effects
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24. Herbal Products: Gingko
Common uses
Prevent memory loss
Vertigo
Tinnitus
May cause GI upset, headache, bleeding
Potential interactions
Aspirin
NSAIDs
Anticoagulants
Anticonvulsants
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25. Classroom Response Question
A 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?
Stomach upset
Diarrhea
Bleeding
Drowsiness
Correct answer: C
Rationale: Potential adverse effects of gingko include stomach or intestinal upset, headache, bleeding, and allergic skin reaction. Potential drug interactions include aspirin, nonsteroidal antiinflammatory drugs (NSAIDs), anticoagulants, and other drugs. The ginkgo may interact with the NSAID medication and cause increased bleeding.
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Nursing Implications
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
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27. Nursing Implications (cont’d)
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
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28. Classroom Response Question
A patient is scheduled to have lunch at The nurse will administer the pyridostigmine (Mestinon) at what time for optimal therapeutic effect?
1100
1130
1200
1230
Correct answer: B
Rationale: The drug should be taken 30 minutes before a meal for maximal therapeutic effect.
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29. Nursing Implications (cont’d)
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
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30. 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?
Administration of physostigmine
Administration of atropine
Administration of epinephrine
Cardiovascular support with dopamine
Correct answer: B
Rationale: Atropine can be given to reverse the effects of an overdose of a cholinergic drug.
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31. Nursing Implications (cont’d)
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
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32. Nursing Implications (cont’d)
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
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33. Nursing Implications (cont’d)
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
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