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40 Cards in this Set
- Front
- Back
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Cholinergic antagonists are sometimes called parasympatholytic, why?
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since they block the actions of the parasympathetic system on effector tissues
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Structure/function of Muscarinic antagonists?
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-atropine and other congeners are tertiary amines
-well absorbed in gut and conjunct membrane, some in skin -after absorb widely distrib throughout body including CNS |
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Muscarinic antagonists that are quaternary amines
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-Ipratropium
-b/c of permanent charge are not readily absorbed/distrib in CNS and have been developed more for peripheral applications such as asthma |
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MOA for antimuscarinic agents
Atropine |
-competitive antagonists at muscarinic receptors, can be overcome w/ higher [agonist]
-sensitive tissues are glands -atropine are non-selective antagonists |
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Why do antimuscarinics have little to no effect at ganglia?
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-ganglionic transmission is mediated by nicotinic receptors
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Antimuscarinic agents and the CNS
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-cause drowsiness and amnesia
-Scopolamine is highly absorbed in CNS--> significant central SEs -at toxic doses--> excitement, agitation, hallucinations and coma |
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Why are antimuscarinic agents useful in the tx of tremor associated w/ Parkinson's disease?
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-they can decrease cholinergic activity in the BG and Striatum
-also useful in tx vestibular disturbances like motion sickness |
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Antimuscarinic agents and the Eye
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-pupillary constrictor m maintains tone by parasymp activity
-if blocked--> symp tone--> mydriasis -caution b/c can precipitate acute glaucoma in a pt w/ a narrow ant chamber angle |
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Cycloplegia
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-anticholinergics block contraction of the ciliary muscle of eye
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Antimuscarinic agents and the Heart
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-mod-high doses of atropine--> tachy
-low doses--> bradycardia b/c at low doses, presynaptic muscarinic receptors (autoreceptors) on vagal nerve terminals are blocked--> no reduction of ACh-->increase vagal tone and bradycardia |
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Antimuscarinic agents and the vasculature
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-effects are relatively slight b/c there is no parasymp innervation
-but muscarinic act can stim release of NO from endo cells-->vasodilation of coronary arteries and symp mediated dilation of skeletal muscle vessels |
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What are the overall effects of antimuscarinic agents on the heart?
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-very small, atropine is limited, maybe some bradycardia
-but it is usefull for blocking or reversing the effects of cholinergic excess on the CVS |
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Antimuscarinic agents and the Respiratory system
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-parasymp innervation through the vagus of bronchiole SM causes constriction and increase in secretions
-atropine will cause slight bronchodil and reduction secretions in normal pt -primary use is during inhalation anesthesia to reduce secretions and prevent laryngospasm |
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Antimuscarinic agents and the GI tract
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-marked reduction in GI smooth muscle motility from the stomach to the colon
-secretions of acid, pepsin and mucin are reduced at very high doses -dry mouth |
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Why can't complete muscarinic blockade totally abolish activity in the GI tract?
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-b/c of influences of hormones and non-cholinergic neurons of the enteric NS
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Antimuscarinic agents and the GU tract
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-relax SM of ureters and bladder
-reduced voiding, useful for treating spasms but may worsen urinary retention |
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Antimuscarinic agents and the sweat glands
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-suppress sweating by blocking sympathetic stim of eccrine sweat glands
-elevation of body temp in infants and children known as "atropine fever" |
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Antimuscarinics and Parkinson's disease
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-weak effect compared w/ levodopa
-reduce tremor but little effect on bradykinesia -used alone or w/ other drugs |
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Some Antimuscarinic agents that can be used to treat drug induced extrapyramidal syndromes
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Bentropine
Biperiden Orphenadrine (congener of Benadryl also used for muscle pain) Trihexyphenidyl |
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Scopalamine
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-used for motion sickness although it causes significant SEs like dry mouth and sedation
-injection, orally, or transdermal patch |
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How is cycloplegia and mydriasis useful?
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-aids in the measurement of refractive error
-facilitates opthalmoscopic exam of the retina |
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If the goal is only mydriasis why should you not use an antimuscarinic drug?
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-b/c of multiple effects
-us an alpha adrenoceptor agonist which is shorter acting |
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Antimuscarinic agents used for opthalmologic uses and their duration of action
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-Scopalamine (3-7 days)
-Atropine (7-10 days) -Homatropine (1-3 days) -Cyclopentolate (1 day) -Tropicamide (.25 days) |
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Tropicamide + Hydroxyamphetamine
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-combines antimuscarinic and sympathomimetic
-good for short term mydriasis |
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Atropine or hyoscyamine use during anesthesia?
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-to inhib increased airway secretions and laryngospasm caused by irritant anesthetics like ether
-SE was an exacerbation of postop urinary retention and intestinal hypomotility |
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COPD and asthma's response to aerosolized antimuscarinics
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-Ipratropium
-Ipratropium and albuterol (bronchodilator effects of muscarinic block and adrenergic activation) -Tiotropium |
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Indication of use of paraenteral atropine
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To prevent
-reflex vagal discharge -increased vagal discharge that occurs intraoperatively, drug-induced -or associated w/ visceral traction stimulation of vagal reflexes |
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Antimuscarinic agents and peptic ulcers
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-rarely used now bc better agents like the proton pump inhibitors (esomeprazole) or hist blockers
-need high doses to reduce gastric secretions--> many SEs -will reduce gastric emptying--> can exacerbate peptic ulcers |
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Antimuscarinic agents that have been seen in clinical use for peptic ulcers
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Atropine
Hyoscyamine Glyopyrrolate |
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Lomotil
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-atropine and diphenoxylate
-antimuscarinics are used as additives to opioid antidirrheals |
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What are two antimuscarinic agents used as antispasmodics?
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-Dicyclomine
-Hyoscyamine |
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What are two antimuscarinic agents used in GU disorders?
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-Oxybutynin
-Tolterodine -used to relieve urinary urgency and intcontinence caused by minor inflammatory bladder disorders and neurologic disorders |
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Why won't "cholinesterase regenerators" like Pralidoxime (PAM) help regenerate central cholinesterases?
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-b/c it is charged and therefore does not cross the BBB
-used for organophosphate activity |
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Rapid onset vs delayed onset mushroom poisoning
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-(15-30 mins) vs (6-12 hrs)
-rapid due to muscarinic excess, tx w/ atropine 1-2mg IV -delayed likely due to amatoxin which damages the liver and kidney, atropine is not helpful here |
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Mneumonic for anticholinergic toxicity
Blind as a bat, dry as a bone, red as a beet, mad as a hatter, hot as a hare, Can't see, can't pee |
-blurred vision
-dry mouth -flushing -confusion -hyperthermia -vision changes -urinary retention |
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What are a couple of contraindications of antimuscarinics?
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-Glaucoma (narrow angle closure glaucoma) and can precipitate acute glaucoma
-in males w/ prostratic hyperplasia |
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Ganglionic Blockade
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-agents that block the actions of ACh on nicotinic receptors present at both symp and parasymp ganglia
-block autonomic outflow-->prevent the reflex activity in the ANS |
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What is the only ganglionic blocker available in the US?
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-Mecamylamine
-competitive antagonists at nicotinic ACh receptors at ganglia and the adrenal medulla -trimethaphan, tetraethylammonium, and hexamethonium are not available |
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Organ systems effects of ganglionic blockade
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-generally the opposite of the dominant division's effects
ex. ganglionic blockade eliminates tone and causes vasodilation of BVs (symp tone dominates) |
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Clinical uses of Mecamylamine
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-moderate to severe hypertension
-orphan drug for Tourtette's syndrome -rarely used but is good for lowering BP in emergency cases of acute dissec AA, b/c of its hypotensive actions and it inhibs symp reflexes |
