Chapter 20

Cholinergic Drugs

• 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.

LEARNING OUTCOMES

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

the sympathetic nervous system (SNS)

CHOLINERGIC DRUGS

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4

The Nervous System

C e n t r a l P e r i p h e r a l

Brain Spinal Cord Somatic(skeletal muscle)A u t o n o m i c

Parasympathetic(cholinergic) ACh

Sympathetic(adrenergic) NE

Alpha Beta

1 2 1 2

zzzzzzzzzzzzzz

“REST & DIGEST”

• Also known as cholinergic agonists or parasympathomimetics

• Mimic effects of the PSNS neurotransmitter acetylcholine (ACh)

CHOLINERGIC DRUGS (CONT’D)

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• Two types, determined by:• Location

• Action once stimulated

• Nicotinic receptors

• Muscarinic receptors

CHOLINERGIC RECEPTORS

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• 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

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• 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

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• 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)

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• 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)

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• Adverse effects are a result of overstimulation of the PSNS

ADVERSE EFFECTS

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System Adverse Effect

CardiovascularBradycardia, hypotension, syncope, conduction abnormalities (e.g., AV Block & Cardiac Arrest)

CNS Headache, dizziness, convulsions, ataxia

GIAbdominal cramps, increased secretions, nausea, vomiting

Respiratory Increased bronchial secretions, bronchospasm

Other Lacrimation, sweating, salivation, miosis

• 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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• 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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• 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)

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A QUESTION

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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 and lead to hypotension, circulatory collapse, bloody diarrhea, shock, and cardiac arrest.

QUESTION

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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

Rationale: Atropine can be given to reverse the effects of an overdose of a cholinergic drug.

ANOTHER QUESTION

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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 cause increased bleeding.

STILL ANOTHER QUESTION

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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 a meal for maximal therapeutic effect.