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) alpha

1 -, alpha 2 -, beta 1 -, or beta 2 -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.

2

CHOLINERGIC DRUGS

• Drugs that stimulate the parasympathetic nervous system (PSNS) • The PSNS is the opposing system to the sympathetic nervous system (SNS) 3

The Nervous System C e n t r a l P e r i p h e r a l Brain Spinal Cord

“

REST & DIGEST” A u t o n o m i c Parasympathetic (cholinergic) ACh Sympathetic (adrenergic) NE

4

1 Alpha 2 Beta 1 2 Somatic (skeletal muscle)

CHOLINERGIC DRUGS (CONT’D)

• • Also known as cholinergic agonists or

parasympathomimetics

Mimic effects of the PSNS neurotransmitter acetylcholine (ACh) 5

CHOLINERGIC RECEPTORS

• • • Two types, determined by: • • Location Action once stimulated Nicotinic receptors Muscarinic receptors 6

NICOTINIC RECEPTORS

• • Located in the ganglia of both the PSNS and SNS Named nicotinic because they can be stimulated by the alkaloid nicotine 7

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 8

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 9

DRUG EFFECTS

• • Effects seen when PSNS is stimulated The PSNS is the “rest and digest” system 10

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 11

CHOLINERGIC DRUG EFFECTS (CONT’D)

• • Cardiovascular effects • • Decreased heart rate Vasodilation Respiratory effects • Bronchial constriction, narrowed airways 12

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 13

INDICATIONS

• Direct-acting drugs • • • Reduce intraocular pressure Useful for glaucoma and intraocular surgery • echothiophate • carbachol • pilocarpine Topical application because of poor oral absorption 14

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 15

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 16

INDICATIONS (CONT’D)

• Indirect-acting anticholinesterase drugs • Used for treatment of mild to moderate Alzheimer’s disease • donepezil (Aricept) • galantamine (Razadyne) • rivastigmine (Exelon) 17

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 GI Respiratory Other

Headache, dizziness, convulsions, ataxia Abdominal cramps, increased secretions, nausea, vomiting Increased bronchial secretions, bronchospasm Lacrimation, sweating, salivation, miosis 18

INTERACTIONS

• • Anticholinergics, antihistamines, sympathomimetics • Antagonize cholinergic drugs, resulting in decreased responses Other cholinergic drugs • Additive effects 19

HERBAL PRODUCTS: GINGKO

• • • Common uses • Prevent memory loss • Vertigo • Tinnitus May cause GI upset, headache, bleeding Potential interactions • • • • Aspirin NSAIDs Anticoagulants Anticonvulsants 20

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 21

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 22

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 23

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 24

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 25

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.

B.

C.

D.

early signs of a cholinergic crisis.

late signs of a cholinergic crisis.

an allergic reaction to the drug.

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.

26

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.

27

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.

B.

C.

D.

Stomach upset Diarrhea Bleeding 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.

28

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.

B.

C.

D.

1100 1130 1200 1230 Rationale: The drug should be taken 30 minutes before a meal for maximal therapeutic effect. 29