Cholinergic Drugs – Flashcards
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Another name for Cholinergic Drugs:
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Parasympathomimetic drugs or Muscarinic Agonists *Bind to muscarinic receptors activating receptors in all effectors organs of the parasympathetic nervous system
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Cholinergic Drug Actions:
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*Decrease intraoccular pressure by constricting pupil and contracting ciliary bodies of the eyes *Heart brake: lower heart rate, decrease output, lowers BP *Dilates blood vessels Skin, Viscera, Mucus Membranes (GI) *Increase tone and motility of GI smooth muscles *Increase peristalsis *Contraction of the detruser muscle bladder increase bladder pressure and relaxes trigone and bladder sphincter = urination
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Common Cholinergic Drug Uses:
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*Eye for glaucoma *Bladder for stimulating urination *Bowels encourage peristalsis *Treatment of Myasthenia gravis *Antagonist to Atropine: reverse effects
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Points to remember with Cholinergic Drugs:
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*Not very selective, therefore.... Side Effects: *Salivation *Bradycardia *Dilation of the blood vessels *Cause abd cramping, NVD *Diaphoresis, flushing *Urgency *To reduce systemic side effects when administering cholinergic eye drops, hold the inner canthus a minute or two to prevent systemic absorption
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Muscarinic Agonist Prototype: Bethanechol (Urecholine, Duvoid) Mechanism of Action:
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*Bethanechol is a direct acting muscarinic agonist. *Binds directly to muscarinic cholinergic receptors and causes activation *At therapeutic doses acts selectively at muscarinic receptors having little or no effects on nicotinic receptors in ganglia or skeletal muscle
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Muscarinic Agonist Prototype: Bethanechol (Urecholine, Duvoid) Pharmacologic Effects: Eyes
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Eye *Miosis (pupillary constriction) *Contraction of the ciliary muscle resulting in accomodation for near vision *The ciliary muscle, which is attached to the lens, focuses the eye for near vision by altering lens curvature. *Decrease intraoccular pressure by constricting pupil and contracting ciliary bodies of the eyes
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Muscarinic Agonist Prototype: Bethanechol (Urecholine, Duvoid) Pharmacologic Effects: Heart
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Heart *Bradycardia
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Muscarinic Agonist Prototype: Bethanechol (Urecholine, Duvoid) Pharmacologic Effects: Exocrine glands
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Exocrine glands *Increase sweating *Increase salivation *Increase Bronchial secretions *Increase secretion of gastric acid
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Muscarinic Agonist Prototype: Bethanechol (Urecholine, Duvoid) Pharmacologic Effects: Smooth muscles
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*Constriction of the bronchi *Increased tone and motility of the GI tract *Contraction of the detrusor muscle & relaxation of the trigone and sphincter results in the emptying of the bladder *Dilation of vascular smooth muscle resulting in lowered BP & possible hypotension
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Muscarinic Agonist Prototype: Bethanechol (Urecholine, Duvoid) Pharmacokinetics:
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*Bethanechol is available for oral administration only! *Effects begin in 30 to 60 minutes and persist about 1 hour *Quaternary ammonium compound that crosses membranes poorly; as a result only a small portion of each dose is absorbed.
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Muscarinic Agonist Prototype: Bethanechol (Urecholine, Duvoid) Therapeutic Uses:
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Urinary Retention (primary use) *Bethanechol is used to treat urinary retention in postoperative and postpartum patients. *Relieves retention by activating muscarinic receptors of the urinary tract resulting in.... *Increased bladder pressure by contracting the detrusor muscle and relaxing the trigone and sphincter muscles *A bedpan or urinal should be readily available
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Muscarinic Agonist Prototype: Bethanechol (Urecholine, Duvoid) Should not be used to treat urinary retention caused by physical obstruction of the urinary tract! Why?
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Because increased pressure in the tract in the presence of blockage could cause injury.
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Muscarinic Agonist Prototype: Bethanechol (Urecholine, Duvoid) Therapeutic Use: Gastrointestinal
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Gastroesophageal Reflux *On an investigational basis *Benefits may result from increased esophageal motility & increased pressure in the lower esophageal sphincter. Can help treat disorders associated with GI paralysis. *Benefits derive from increased tone and motility of GI smooth muscles. *Specific applications: adynamic ileus, gastric atony, & postoperative abdominal distention *Should not be given if physical obstruction in GI tract
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Muscarinic Agonist Prototype: Bethanechol (Urecholine, Duvoid) Adverse Effects: Heart
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Relatively Rare with oral dosing! *Hypotension and bradycardia: contraindicated for patients with low blood pressure or low cardiac output
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Muscarinic Agonist Prototype: Bethanechol (Urecholine, Duvoid) Adverse Effects: GI tract
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At usual therapeutic doses, Bethanechol can cause: *Excessive salivation *Increased secretion of gastric acid *Abdominal cramps *Diarrhea At higher doses can cause: *Involuntary defecation Contraindicated: *Patients with gastric ulcers *Intestinal obstruction *Recovering from recent bowel surgery
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Muscarinic Agonist Prototype: Bethanechol (Urecholine, Duvoid) Adverse Effects: Urinary Tract
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Contraindicated: *Patients with urinary tract obstruction *Weakness in bladder wall Reason: Because of its ability to contract the bladder detrusor, and thereby increase pressure within the urinary tract it could lead to rupture of the bladder
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Muscarinic Agonist Prototype: Bethanechol (Urecholine, Duvoid) Adverse Effects: Exacerbation of Asthma
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*By activating muscarinic receptors in the lungs, bethanechol can cause bronchoconstriction. *Contraindicated in patients with latent or active asthma
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Muscarinic Agonist Prototype: Bethanechol (Urecholine, Duvoid) Adverse Effects: Dysrhythmias in Hyperthyroid Patients
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*May increase heart rate to the point of initiating a dysrhythmia: opposite to the effect that muscarinic agonists have in most patients *Initial cardiovascular response is normal: bradycardia and hypotension. *In reaction to hypotension the baroreceptor reflex attempts to normalize BP. Reflex involves release of Norepi from sympathetic nerves that regulate the heart. In Non-Hyperthyroid pts Norepi helps increase output & normalize BP *Hyperthyroid Pts extremely sensitive to Norepi so relatively small amts can overstimulate & elicite a dysrhythmia
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Muscarinic Agonist Prototype: Bethanechol (Urecholine, Duvoid) Preparations, Dosage, and Administration
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Available in tablets: 5, 10, 25, 50 mg for oral therapy Adults: 10 to 50mg given 3 to 4 times a day Administration with meals can cause nausea & vomiting and hence dosing should be done one hour before meals or 2 hours after meals
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Muscarinic Agonist: Pilocarpine (Isoptocarpine) Trade name: Salagen
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Therapeutic Use: *Topical therapy of glaucoma *Oral therapy of dry mouth resulting from Sjogren's syndrome, or from salivary gland damage caused by radiation therapy of head & neck cancer Principle Adverse Effects: *Sweating in 29% patients with recommended dose 5mg 3 to 4 times a day *If dosage is excessive can produce full spectrum of muscarinic effects
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Muscarinic Agonist: Pilocarpine (Isoptocarpine) Trade Name: Salagen Effects on the Eye? *Miosis via constriction of the pupil via contraction of the iris sphincter *Contraction of the ciliary muscle: an action that focuses the lens for near vision *IOP lowered indirectly Effects on open angle glaucoma? Effects on angle-closure glaucoma?
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Effects on the Eye: *Pt's w/ open angle glaucoma, IOP reduced because the tension generated by contracting ciliary muscle promotes widening of the spaces w/in the trabecular meshwork, facilitating outflow of aqueous humor *Angle-closure glaucoma, contraction of the iris sphincter pulls iris away from the pores of the trabecular meshwork, removing the impediment to aqueous humor outflow
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Muscarinic Agonist: Pilocarpine (Isoptocarpine) Trade Name: Salagen Therapeutic Uses?
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Therapeutic Uses: *2nd line drug for open-angle glaucoma *Emergency treatment of acute angle-closure glaucoma
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Muscarinic Agonist: Pilocarpine (Isoptocarpine) Trade Name: Salagen Adverse Effects?
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*Occasionally, sustained contraction of the ciliary muscle causes retinal detachment *Focuses the lens for near vision: corrective lenses can provide partial compensation for this problem (blurry vision) *Constriction of the pupil may decrease visual acuity *May produce local irritation, eye pain, & brow ache *Severe side effects can be reversed with atropine muscarinic antagonist
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Muscaranic Agonists Generic Name: Bethanechol Chloride Trade Names:
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*Duvoid *Urecholine
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Muscarinic Agonists Generic Name: Pilocarpine Trade Names:
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Salegen
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Muscarinic Agonists Generic Name: Physostigmine Salicylate *AChE inhibitor Trade Names:
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*Eserine *Antilirium Uses: *Reversal of anticholinergic excess *Antidote to Atropine overdose *Antidote to Curare
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Muscarinic Agonists Generic Name: Pyridostigmine *AChE inhibitor Trade Names:
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*Mestinon *Regonal Uses: *Increase muscle strength in the symptomatic treatment of myasthenia gravis *Reversal of nondepolarizing neuromuscular blocking agents *Prophylaxis of lethal effects of poisening with the nerve agent soman
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Muscarinic Agonists Generic Name: Neostigmine *AChE inhibitor Trade Name:
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*Prostigmin Uses: *Improvement in muscle strength in symptomatic treatment of myasthenia gravis *Prevention and treatment of postoperative bladder distention and urinary retention or ileus *Reversal of nondepolarizing neuromuscular blockers *Antidote to Curare
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Muscarinic Agonists Generic Name: Edrophonium *AChE inhibitor Trade Name:
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*Tensilon *Enlon Uses: *Diagnosis of myasthenia gravis *Assessment of adequacy of anticholinesterase therapy in myasthenia gravis *Differentiating myasthenic from cholinergic crisis *Reversal of muscle paralysis from nondepolarizing neuromuscular blocking agents
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Sources of Muscarinic Poisening
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*Overdose of direct acting muscarinic agents such as bethanechol and pilocarpine *Overdose cholinesterase inhibitors
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Symptoms of Muscarinic Poisening
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*Profuse salivation *Lacrimation *Visual disturbances *Bronchospasms *Diarrhea *Bradycardia *Hypotension *Severe poisening can produce cardiovascular collapse
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Treatment for Muscarinic Poisening
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*Administration of Atropine: by blocking muscarinic receptors can reverse most signs of toxicity *Provide supportive therapy
