cholinergic agonists - Nursing Pharmacology

Report
Chapter 20
Cholinergic Drugs
LEARNING OUTCOMES
•
1. Identify the basic functions of the nervous system.
•
2. Identify divisions of the peripheral nervous system.
•
3. Compare and contrast the actions of the sympathetic and parasympathetic divisions of the autonomic nervous
system.
•
4. Compare and contrast the types of responses that occur when drugs activate (or block) alpha1-, alpha2-,
beta1-, or beta2-adrenergic receptors, and nicotinic or muscarinic receptors.
•
5. Discuss the classification and naming of autonomic drugs based on four possible actions.
•
6. Describe the nurse’s role in the pharmacological management of patients receiving drugs affecting the
autonomic nervous system.
•
7. Use the nursing process to care for patients receiving adrenergic agents, adrenergic-blocking agents,
cholinergic agents, and cholinergic-blocking agents.
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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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The Nervous System
Central
Brain
Peripheral
Spinal Cord
“REST & DIGEST”
Somatic
Autonomic
(skeletal muscle)
Sympathetic
(adrenergic) NE
Parasympathetic
(cholinergic) ACh
Alpha
4
1
Beta
2
1
2
CHOLINERGIC DRUGS (CONT’D)
• Also known as cholinergic agonists or
parasympathomimetics
• Mimic effects of the PSNS neurotransmitter acetylcholine
(ACh)
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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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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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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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CHOLINERGIC DRUG EFFECTS (CONT’D)
• Cardiovascular effects
• Decreased heart rate
• Vasodilation
• Respiratory effects
• Bronchial constriction, narrowed airways
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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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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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ADVERSE EFFECTS
• Adverse effects are a result of overstimulation of the
PSNS
System
Adverse Effect
Cardiovascular
Bradycardia, hypotension, syncope,
conduction abnormalities (e.g., AV Block &
Cardiac Arrest)
CNS
Headache, dizziness, convulsions, ataxia
GI
Abdominal cramps, increased secretions,
nausea, vomiting
Respiratory
Increased bronchial secretions,
bronchospasm
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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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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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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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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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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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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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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A 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
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.
Rationale: The items listed are early signs of a cholinergic crisis, which can become more severe
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and lead to hypotension, circulatory collapse, bloody diarrhea, shock, and cardiac arrest.
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.
B.
C.
D.
Administration of physostigmine
Administration of atropine
Administration of epinephrine
Cardiovascular support with dopamine
Rationale: Atropine can be given to reverse the effects of an
overdose of a cholinergic drug.
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ANOTHER 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?
A. Stomach upset
B. Diarrhea
C. Bleeding
D. Drowsiness
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
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cause increased bleeding.
STILL ANOTHER 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
Rationale: The drug should be taken 30 minutes before
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a meal for maximal therapeutic effect.

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