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Chapter 14

Chapter 14. Muscarinic Agonists and Antagonists. Cholinergic Drugs. Agents that influence the activity of cholinergic receptors Most mimic or block the actions of acetylcholine. Cholinesterase inhibitors Indirectly prevent the breakdown of acetylcholine. Cholinergic Drugs.

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Chapter 14

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  1. Chapter 14 Muscarinic Agonists and Antagonists

  2. Cholinergic Drugs • Agents that influence the activity of cholinergic receptors • Most mimic or block the actions of acetylcholine. • Cholinesterase inhibitors • Indirectly prevent the breakdown of acetylcholine

  3. Cholinergic Drugs • Toxicology encompasses • Nicotine • Insecticides • Chemical warfare

  4. Tips for Understanding the Cholinergic Drugs • Know the receptors that the drug affects. • Know the normal responses to activation of those receptors. • Know whether the drug in question increases or decreases receptor activation.

  5. Master Keys to Cholinergic Drugs

  6. Master Keys to Cholinergic Drugs

  7. Muscarinic Agonists and Antagonists • Muscarinic agonists • Bethanechol • Other muscarinic agonists • Toxicology of muscarinic agonists • Muscarinic antagonists (anticholinergic drugs) • Atropine • Anticholinergic drugs for overactive bladder (urge incontinence) • Other muscarinic antagonists • Toxicology of muscarinic antagonists

  8. Tips for Understanding the Cholinergic Drugs • Bethanechol (prototype drug) • Selective agonist at muscarinic cholinergic receptors • Refer to Table 14-2. • Note the effects muscarinic receptors can produce. • Bethanechol activates muscarinic receptors (agonist). • Know which receptors a drug interacts with (Table 14-2) and what those receptors do (Table 14-2). • You can predict the types of responses you might expect from bethanechol.

  9. Muscarinic Agonists and Antagonists • Muscarinic agonists • Bethanechol • Other muscarinic agonists • Toxicology of muscarinic agonists

  10. Muscarinic Agonists and Antagonists • Principal structures affected by muscarinic activation • Heart: bradycardia • Exocrine glands: increase sweating, salivation, bronchial secretions, and secretion of gastric acid • Smooth muscles • Contraction in lung (constriction) • GI tract (increased tone/motility) • Bladder (contraction of detrusor) • Vascular (relaxation, vasodilation, hypotension) • Eye (pupillary constriction and ciliary contraction)

  11. Muscarinic Agonists • Bethanechol • Mechanism of action • Pharmacologic effects • Pharmacokinetics • Therapeutic uses • Urinary retention • Gastrointestinal uses

  12. Muscarinic Agonists • Adverse effects • Cardiovascular system • Alimentary system • Urinary tract • Exacerbation of asthma • Dysrhythmias in hyperthyroid patients • Preparations, dosage, and administration

  13. Fig. 14-1. Structures of muscarinic agonists.

  14. Other Muscarinic Agonists • Cevimeline • Actions and uses • Adverse effects • Drug interactions • Preparations, dosage, and administration

  15. Other Muscarinic Agonists • Pilocarpine • Glaucoma • Acetylcholine • Miosis • Muscarine • Present in poisonous mushrooms

  16. Overactive Bladder • Also known as urgency incontinence, detrusor instability, and sometimes “can’t-hold-it-anymore” incontinence • Four major symptoms: urinary urgency, urinary frequency, nocturia, and urge incontinence • Urge incontinence often results from involuntary contractions of the bladder detrusor.

  17. Overactive Bladder • Affects up to one-third of Americans • Can develop at any age, but is most predominant in elderly patients • Two modes of treatment: behavioral therapy and drug therapy • If ineffective—percutaneous tibial nerve stimulation (PTNS) may be tried.

  18. Muscarinic Antagonists(Anticholinergic Drugs) • Competitively block the actions of acetylcholine at muscarinic receptors • Most muscarinic receptors on structures innervated by parasympathetic nerves • Also known as parasympatholytic drugs, antimuscarinic drugs, muscarinic blockers, and anticholinergic drugs • Anticholinergic drugs: produce selective blockade of muscarinic receptors—not all cholinergic receptors

  19. Muscarinic Antagonists(Anticholinergic Drugs) • Certain drugs (antihistamines, tricyclic antidepressants, phenothiazine antipsychotics) have prominent antimuscarinic actions. • Use with caution—or not at all—with patients receiving other muscarinic antagonists.

  20. Muscarinic Antagonists(Anticholinergic Drugs) • Atropine • Best known muscarinic antagonist • Found in nature • Mechanism of action • No direct effect of its own • Muscarinic receptor blockade

  21. Muscarinic Antagonists(Anticholinergic Drugs) • Atropine • Pharmacologic effects (receptor blockade) • Heart • Exocrine glands • Smooth muscle • Eye • CNS • Dose dependency of muscarinic blockade • Pharmacokinetics

  22. Muscarinic Antagonists(Anticholinergic Drugs) • Atropine (cont’d) • Therapeutic uses • Preanesthetic medication • Disorders of the eye • Bradycardia • Intestinal hypertonicity and hypermotility • Muscarinic agonist poisoning • Peptic ulcer disease • Asthma • Biliary colic

  23. Muscarinic Antagonists(Anticholinergic Drugs) • Atropine (cont’d) • Adverse effects • Xerostomia (dry mouth) • Blurred vision and photophobia • Elevation of intraocular pressure • Urinary retention • Constipation • Anhidrosis • Tachycardia • Asthma

  24. Muscarinic Antagonists(Anticholinergic Drugs) • Atropine (cont’d) • Drug interactions • Avoid combining atropine with other drugs capable of causing muscarinic blockade • Preparations, dosage, and administration • General systemic therapy • AtroPen for cholinesterase inhibitor poisoning • Ophthalmology

  25. Anticholinergic Drugs for Overactive Bladder • Overactive bladder (OAB): characteristics and overview of treatment • Introduction to anticholinergic therapy of OAB • Specific anticholinergic drugs for OAB • Oxybutynin (Ditropan, Oxytrol, Gelnique) • Syrup • Extended-release tablets • Transdermal patch and gel

  26. Anticholinergic Drugs for Overactive Bladder • Specific anticholinergic drugs for OAB (cont’d) • Darifenacin • Solifenacin • Tolterodine • Immediate-release tablets • Extended-release capsules • Trospium • Fesoterodine

  27. Other Muscarinic Antagonists • Scopolamine • Ipratropium bromide • Antisecretory anticholinergics • Dicyclomine • Pirenzepine and telenzepine • Mydriatic-cycloplegics • Centrally acting anticholinergics

  28. Toxicology of Muscarinic Agonists • Source of muscarinic poisoning • Direct-acting muscarinic agonists • Cholinesterase inhibitors • Symptoms • Result from excessive activation of muscarinic receptors • Treatment • Muscarinic blocking agent, such as atropine

  29. Toxicology of Muscarinic Antagonists • Sources of antimuscarinic poisoning • Natural products • Selective antimuscarinic drugs • Drugs with pronounced antimuscarinic properties

  30. Toxicology of Muscarinic Antagonists • Symptoms • Dry mouth • Blurred vision • Photophobia • Hyperthermia • CNS effects • Hot, dry, and flushed skin

  31. Toxicology of Muscarinic Antagonists • Treatment • Physostigmine • Inhibitor of acetylcholinesterase • Warning • Differentiate between poisoning and an actual psychotic episode!

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