chapter 20 cholinergic drugs copyright © 2014 by mosby, an imprint of elsevier inc

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

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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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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)

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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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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.

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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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memantine (Namenda) Not a cholinergic drug Also used in the treatment of Alzheimer’s disease

Indications (cont’d)

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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

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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

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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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