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muscarinic receptor locations:
sweat glands, blood vessels, all organs of parasympathetic nervous system
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nicotinic N receptor locations:
all ganglia of the autonomic nervous sx.
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Nicotinic M receptor location:
neuromuscular junction
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effects of muscarinic receptor activation:
decrease heart rate, increase gland secretion, smooth muscle contraction
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effects of nicotinic M receptor activation:
promotes ganglionic transmission
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muscarinic receptor agonists:
- bethanecol
- choinesterase inhibitors: physostigmine, neostigmine
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muscarinic receptor antagonists:
atropine
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effects of nicotinic N receptor activation:
promotes ganglionic transmission
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nicotinic N receptor agonists:
nicotine
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nicotinic N receptor antagonists:
mecamylamine
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receptor location for nicotinic M:
neuromuscular junciton
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Nicotinic M effects of receptor activation:
skeletal muscle contraction
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nicotinic M receptor agonists:
nicotine (must be in much higher doses than nicotinic n receptors)
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nicotinic M receptor antagonists:
d-Tubocurarine, succynilcholine
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muscarinic agonists are also known as:
parasympathomimetic agents
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Bethanecol (urecholine) mechanism of action:
direct acting muscarinic agonist, binds reversibly to muscarinic cholinergic receptors and causes activation
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pharmacologic effects of Bethanecol:
- muscarinic effects:
- bradychardia
- increase secretions including sweat
- GI motility
- bladdy emptying
- vascular dilation
- pupil constriciton
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pharmacokinetics of bethanecol:
- oral administration only
- effects begin 30-60 min after admin.
- crosses membranes poorly and therefore only a small portion of administered dose is absorbed
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therapeutic use of Bethanecol:
- urinary retention
- GI- investigational basis for gastroesohageal reflux
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bethanecol adverse effects:
- cardiovascular: hypotension and bradychardia
- GI: increase motility, diahrrea, excess salivation, increase gastric acid
- lungs: exacerbation of asthma from bronchoconstriction
- urinary tract: increases pressure in bladder and causes voiding
- thyroid pts- causes dysrythmias
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Bethanecol preparations, dosages and administration:
- available in tablets 5,10,25,50; for adults 10-50mg q 3-4x daily
- given an hour before or 2 hours after a meal because it causes vomiting and nausea
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Cevimeline (Evovax):
- for relief of xerostomia caused by Sjogren's syndrome
- activates muscarinic receptors
adverse: same as muscarinic activation- excess sweating, nausea, rhinitis, diarrhea
contraindicated: uncontrolled asthma
drug interaction: intensifies cardiac depression from beta blockers(both drugs decrease heart rate)
preparations: 30mg capsules, dose=30mg x3 daily
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Pilocarpine (Salagen):
is a muscarine agonist for topical therapy of glaucoma and oral therapy of dry mouth
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acetylcholine (Miochol-E):
- primarily acts to produce rapid pupil constriciton,
- lacks selectivity
- extremely short half life
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muscarine:
- not used clinically
- has role in discoery of cholinergic receptor cybtypes
- toxic and found in certain mushrooms
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sources for muscarinic poisoning:
certain mushrooms, OD from direct-acting muscarinic agonists (bethanecol, pilocarpine) and cholinesterase inhibitors
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symptoms of muscarinic poisoning:
profuse salivation, lacrimation, visual disturbances, bronchospasm, diarrhea, bradycardia, hypotension
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treatment of muscarinic poisoning:
atropine becuase it is selective and blocks the receptors for muscarine and it reverses the signs of toxicity
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muscarinic antagonists (anticholinergic drugs):
- atropine
- OAB DRUGS:(overactive bladder)
- -oxybutinin-Ditropan, Ditropan XL, Oxytrol
- -darifenacin-Enablex
- -solifenacin-Vesicare
- -tolterodine-Detrol, Detrol LA
- -trospium-Santura, Sanctura XR
- scopolamine
- ipatropium bromide
- antisecretory anticholinergics
- dicyclomine
- pirenzepine
- telenzepine
- mydriatic cycloplegics
- centrally acting cholinergics
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sources of antimuscarinic poisoning:
- atropa belladonna
- datura stramonium
- antihistamines
- phenothiazines
- tricyclic antidepressants
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symptoms of antimuscarinic poisining:
- direct result of muscarinic blockade:
- dry mouth, blurred vision, photophobia, hyperthermia, CNS effects, skin that it hot,dry and flush
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