CHAPTER 19 Cholinergic Drugs Mosby items and derived

Cholinergic Drugs: Definition Drugs that stimulate the parasympathetic nervous system (PSNS) The PSNS is the opposing system to the SNS Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Cholinergic Drugs: Definition (cont’d) Also known as cholinergic agonists or parasympathomimetics Mimic the effects of the PSNS neurotransmitter: acetylcholine (ACh) Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an

Cholinergic Receptors Two types, determined by: Location Ø Action once stimulated Ø Nicotinic receptors Muscarinic receptors Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Nicotinic Receptors Located in the ganglia of both the PSNS and SNS Named “nicotinic” because it can be stimulated by the alkaloid nicotine Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Muscarinic Receptors Located postsynaptically in the effector organs of the PSNS Smooth muscle Ø Cardiac muscle Ø Glands Ø Named “muscarinic” because it can be stimulated by the alkaloid muscarine Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Mechanism of Action Direct-acting cholinergic agonists Ø Bind to cholinergic receptors, activating them Mosby

Mechanism of Action (cont’d) Indirect-acting cholinergic agonists Inhibit the enzyme acetylcholinesterase, which breaks down ACh Ø Result: more ACh is available at the receptors Ø Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Indirect-Acting (Cholinesterase Inhibitors) Reversible Ø Bind to cholinesterase for a period of minutes to hours Irreversible Bind to cholinesterase and form a permanent covalent bond Ø The body must make new cholinesterase to break these bonds Ø Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Drug Effects seen when the PSNS is stimulated The PSNS is the “rest and

Drug Effects (cont’d) “SLUDGE” Salivation Lacrimation Urinary incontinence Diarrhea Gastrointestinal cramps Emesis Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Drug Effects (cont’d) Stimulate intestine and bladder Ø Increased gastric secretions Ø Increased gastrointestinal motility Ø Increased urinary frequency Stimulate pupils Ø Constriction (miosis) Ø Reduced intraocular pressure Increased salivation and sweating Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Drug Effects (cont’d) Cardiovascular effects Decreased heart rate Ø Vasodilation Ø Respiratory effects Ø Bronchial constriction, narrowed airways Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Drug Effects (cont’d) At recommended doses, the cholinergics primarily affect the muscarinic receptors At high doses, cholinergics stimulate the nicotinic receptors Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Drug Effects (cont’d) Desired effects: from muscarinic receptor stimulation Many undesirable effects are due to stimulation of the nicotinic receptors Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Indications Direct-acting drugs Reduce intraocular pressure Useful for glaucoma and intraocular surgery Ø Examples: acetylcholine, carbachol, pilocarpine Topical application due to poor oral absorption Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

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 SC injection Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

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) Ø Examples: physostigmine, pyridostigmine Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Indications (cont’d) Indirect-acting drugs—cevimeline (Evoxac) Used to treat xerostomia (dry mouth) resulting from Sjögren’s syndrome Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Adverse Effects Adverse effects are a result of overstimulation of the PSNS Cardiovascular Ø CNS Ø Bradycardia, hypotension, conduction abnormalities (AV block and cardiac arrest) Headache, dizziness, convulsions Gastrointestinal Ø Abdominal cramps, increased secretions, nausea, vomiting Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Adverse Effects (cont’d) Respiratory Ø Increased bronchial secretions, bronchospasms Other Ø Lacrimation, sweating, salivation, loss of binocular accommodation, miosis Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Interactions Anticholinergics, antihistamines, sympathomimetics Ø Antagonize cholinergic drugs, resulting in decreased responses Other cholinergic drugs Ø Additive effects Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Nursing Implications Keep in mind 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 Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Nursing Implications (cont’d) Medications should be taken as ordered and not abruptly stopped The doses should be spread evenly apart to optimize the effects of the medication Overdosing can cause life-threatening problems. Patients should not adjust the dosages unless directed by the physician Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

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 Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Nursing Implications (cont’d) Atropine is the antidote for cholinergics. 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 Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Nursing Implications (cont’d) Monitor for therapeutic effects Alleviated signs and symptoms of myasthenia gravis In postoperative patients with decreased GI peristalsis, look for: Ø Increased bowel sounds Ø Passage of flatus Ø Occurrence of bowel movements Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.

Nursing Implications (cont’d) Monitor for therapeutic effects (cont’d) In patients with urinary retention/hypotonic bladder, urination should occur within 60 minutes of bethanechol administration ALSO monitor for adverse effects Mosby items and derived items © 2007, 2005, 2002 by Mosby, Inc. , an affiliate of Elsevier Inc.