Term
Acetylcholine blocking agents: Cholinergic Neuron Blockers:
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Definition
–hemicholinium
•blocks transport of choline into neuron
–results in ¯ release of ACh
–botulinium toxin (food poisoning)
•blocks the nerve-stimulated release of acetylcholine
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Term
Acetylcholine blocking agents: •Ganglionic Blockers:
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Definition
–block nicotinic receptors of sympathetic and parasympathetic autonomic ganglia and adrenal medulla
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Term
Acetylcholine blocking agents:•Neuromuscular Blockers: (curare) |
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Definition
–block nicotinic receptors on motor end plates of skeletal muscle fibers
•Belladonna alkaloids (atropine, scopolamine)
–competitive antagonists of acetylcholine and other muscarinic receptor agonists
–usually little or no effect at nicotinic receptors
–not all muscarinic receptors are equally sensitive to the effect of these drugs (may be related to high and low affinity binding sites)
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Term
Pharmacological Properties of Antimuscarinic Drugs: Salivary Glands |
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Definition
Salivary Glands
•highly sensitive, resulting in dry mouth with difficulty swallowing and talking at low doses
•completely abolish para-sympathetically-induced secretions
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Term
Pharmacological Properties of Antimuscarinic Drugs: Sweat Glands |
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Definition
Sweat Glands
•cholinergic innervations although part of the sympathetic nervous system
•highly sensitive, skin hot and dry, body temperature may rise (with toxic doses)
•“atropine fever” can be induced in infants (temperature may reach 43°C)
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Term
Pharmacological Properties of Antimuscarinic Drugs: Eyes |
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Definition
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Eye
•iris - dilation of circular muscle
–mydriasis, photophobia
–blocks effects of ACh at sphincter and ciliary muscles
•ciliary muscle - relaxation
•paralysis of accommodation (cycloplegia)
–the lens is fixed for far vision (near objects appear blurred)
•loss of normal pupillary response (contraction) to light
•little or no effect on intraocular pressure except in narrow angle glaucoma
– due to an increase in aqueous outflow resistance
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Term
Pharmacological Properties of Antimuscarinic Drugs: Cardiovascular System (Heart) |
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Definition
Cardiovascular System
•heart (main effect is on heart rate)
–low doses - decrease rate by centrally stimulating the vagus nerve (¯ 4-8 beats/min)
•rarely a significant effect
–higher doses - result in increasing tachycardia by blocking vagal effects on the S-A nodal pacemaker
•more apparent in young adults with increased vagal tone - 35-40 beats/min at rest
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Term
Pharmacological Properties of Antimuscarinic Drugs: Cardiovascular System (Circulation) |
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Definition
Cardiovascular System
•circulation
–usually only toxic doses result in dilation of cutaneous blood vessels
•atropine flush - has been mistaken for Scarlet Fever
–counteracts peripheral vasodilatation and sharp fall in blood pressure caused by choline esters
–little effect when given alone
–no cholinergic innervations of blood vessels
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Term
Pharmacological Properties of Antimuscarinic Drugs: Respiratory System |
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Definition
Respiratory Tract
•inhibition of secretions of nose, pharynx and bronchi so that these drugs dry the mucus membranes of the respiratory tract.
•bronchodilation
•relaxation of smooth muscles
•increases volume of residual air (dead space) leading to respiratory stimulation
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Term
Pharmacological Properties of Antimuscarinic Drugs: GI Tract |
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Definition
Gastrointestinal Tract
•reduction of gastric secretions
–reduced volume and total acid content
•usually only seen with high doses that also affect other systems (dry mouth, etc.)
•inhibition of gastric motility
–decreased tone and amplitude of peristalic contractions
•also only seen with relatively high doses
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Term
Pharmacological Properties of Antimuscarinic Drugs: Urinary Tract |
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Definition
Urinary Tract
•urinary retention
–relaxation of the detrusor muscle
•relaxation of the ureter
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Term
Pharmacological Properties of Antimuscarinic Drugs: CNS |
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Definition
Central Nervous System
•decreased concentration and memory
•drowsiness and sedation
•excitation
•ataxia
•hallucinations
•coma
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Term
Poisoning due to the Ingestion of Antimuscarinic Drugs |
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Definition
•the deliberate or accidental ingestion of belladonna alkaloids or drugs with “atropine-like” properties is a major cause of poisoning
•infants and small children are susceptible
•can be fatal
–respiratory and/or circulatory arrest
–10 mg or less in children can be fatal
•diagnose poisoning by administering an AChE inhibitor
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Term
Other Drugs with
Antimuscarinic Properties: |
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Definition
•antihistamines
•antidepressants (tricyclic antidepressants)
•antipsychotics (chlorpromazine)
•antiparkinsonian agents (benztropine)
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Term
Therapeutic Uses of Antimuscarinic Drugs: Preanesthetic Medication |
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Definition
Preanesthetic Medication
•inhibit excessive salivation and secretions of respiratory tract (atropine)
–often administered prior to a general anesthetic to prevent choking or drowning on the respiratory secretions
•bronchodilator effects
–increases ventilation of the lungs
•tranquilization and amnesia (sedation)
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Term
Therapeutic Uses of Antimuscarinic Drugs: Opthalmology |
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Definition
Ophthalmology
•local administration
–topical aqueous solution to limit effects to the eye
•mydriasis
–dilation of pupil necessary for a thorough examination of retina and optic disk
•cycloplegia (cyclopentolate)
–to measure refractive index of the eye
•contraindicated in narrow angle glaucoma
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Term
Therapeutic Uses of Antimuscarinic Drugs: GI Tract |
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Definition
Gastrointestinal Tract
•peptic ulcer (although not always the best therapy)
–histamine H2 receptor blockers are more effective
–patient compliance can be a problem due to side effects (dry mouth, blurred vision, etc.)
•spasticity of GI tract (propantheline)
–best if condition results from excessive parasympathetic stimulation
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Term
Therapeutic Uses of Antimuscarinic Drugs: CNS Actions |
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Definition
CNS actions
•parkinsonism-like symptoms induced by antipsychotic therapy (benztropine)
–especially the phenothiazines and butyrophenones
–levodopa is the drug of choice for Parkinson’s Disease
–However, cannot use levodopa to treat antipsychotic-induced parkinsonism
•motion sickness (scopolamine)
–among the first drugs used to prevent motion sickness
•obstetrical sedation
–sedation , tranquilization and amnesia are produced when administered in combination with other agents for analgesia and sedation
•found in many over-the-counter “sleeping pills” due to sedative effects
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Term
Therapeutic Uses of Antimuscarinic Drugs: Respiratory Sytem |
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Definition
Respiratory Tract
•reduce secretions in both upper and lower respiratory tract
•used in many over-the-counter “cold” mixtures (atropine and scopolamine)
–for symptomatic relief of acute rhinitis associated with hay fever
–does not affect the natural course of the condition
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