Muscarinic antagonists Flashcards
muscarinic antagonists generally
block the effects of ACh at M1, M2, M3, antagonizing parasympathetic stimulation
atropine and scopolamine are found in
atropine is also found in
belladonna plant
jimson weed
atropine CNS effects
NONE except at toxic doses.
therefore mostly has peripheral effects
scopolamine CNS effects
enters CNS easily –> sedation, amnesia, euphoria (can be abused)
scopolamine is well absorbed ________, and is used for _________
through the skin
transdermal patch for motion sickness
at low doses of atropine, the main effects are
dry mouth, decreased sweating
as atropine dose is increased effects include
tachycardia, blurred vision, palpitations
at moderately high (but not high enough to penetrate CNS) doses, atropine causes
urinary retention, hot and dry skin, restlessness, fatigue
when toxic doses of atropine penetrate the CNS, it causes
ataxia, hallucinations, delirium, coma, rapid and weak pulse
common drugs that block muscarinic receptors and might be seen in poisoning
antihistamines, antidepressants, and antipsychotics
low doses of scopolamine CNS effects
drowsiness, amnesia
toxic doses scopolamine effects
excitement, agitation, hallucinations, coma
why would scopolamine be used for pre-anesthesia
sedation, amnesia, decrease sedations
situations where DA receptors are blocked or DA is reduced causing imbalance of ACh/DA in the corpus striatium
Antipsychotic drugs
Parkinsons
3 antimuscarinics used to restore the ACh/DA balance in the corpus striatum
trihexyphenidyl, benztropine, diphenhydramine
in the elderly, antimuscarinic drugs cause
memory impairment, delirium, dementia
risks of long term antimuscarinic use
Alzheimer’s
antimuscarinic effects on the eye
block circular muscle --> mydriasis block ciliary muscle --> cycloplegia block reflex to light --> photophobia block lacrimation --> dry eyestac (used for eye exams)
loss of accommodation is called
cycloplegia
contraindications to the use of antimuscarinics, and why
narrow angle glaucoma
blockage of ciliary muscle –> closed trabecular system –> increased intraocular pressure
antimuscarinics cause tachycardia because
Presynaptic M2 autoreceptors are blocked –> increased NE
Postsynaptic M2 autoreceptors are blocked –> vagal effects (reflex bradycardia) removed
tachycardia due to antimuscarinics is most noticeable in ________ and least noticeable in ________ due to __________
healthy young adults
elderly, babies
they have little vagal tone
drug used to prevent vagal bradycardia when visceral organs are being handled during surgery
glycopyrrolate
drug used in MI to decrease bradycardia or MI block
atropine
reflex vagal discharge
due to pain, stimulation of carotid sinus, pressure on the eyeballs, irritation of the larynx during intubation —-> and AV node depression —> bradycardia, decreased CO
used to reverse reflex vagal discharge
atropine
used to reverse bradycardia produced by muscarinic agonists/cholinesterase inhibitors
atropine
used to block decrease in blood pressure seen with IV muscarinic agonists at M3 receptors
atropine
M3 receptors on endothelial cells cause vasodilation by
releasing nitric oxide in response to a muscarinic agonist
toxic doses of atropine cause _______ because _______
vasodilation in the face
happens to offload excess heat since sweating is blocked
antimuscarinics, pre-anesthia respiratory effects
inhibit secretions of salivary gland/respiratory tract
decrease laryngospasm
compounds use in the lung are
quaternary ammonium compounds, inhaled w/o systemic absorption.
ipratropium and tirtropium are
bronchodilators for asthma, COPD
antispasmodics
drugs that decrease motility and secretions in GI tract
commonly used antispasmodic
dicyclomine
treatment of diarrhea that has low potential for abuse because of side effects with higher doses
atropine (blocks GI)
+
diphenoxylate (opioid, synergistically blocks GI)
name for atropine + diphenoxylate
lomotil
diphenoxylate is an
opioid
drug to decrease bladder overactivity
tolterodine
tolterodine is the preferred drug for bladder control in the elderly in whom muscarinic blockade can cause delirium because
M3 specific –> few side effects
No CNS effects
drugs that are similar to tolterodine
fesoterodine, darifenacin, solifenacin
drug used to prevent bladder spasm after prostate surgery
oxybutnin
drug used to prevent bladder spasm after prostate surgery that causes less dry mouth
tropspium
use for glycopyrrolate (outside the OR)
decrease muscarinic effects of AChE inhibitors in MG patients
contraindication of antimuscarinics in old men
BPH due to increased urinary retention
what’s that weird saying for atropine poisoning
dry as a bone, blind as a bat, mad as a hatter, red as a beet
who’s sensitive af to atropine poisoning and why
infants/children due to sensitivity to hyperthermia
symptoms of atropine poisoning
dry mouth, mydriasis, tachycardia, decreased bowel sounds, hot flushed skin, agitation, delirum
scopolamine poisoning, for added fun, causes
atropine poisoning effects + toxic psychosis (it enter CNS)
treatment for atropine poisoning and reasoning
systemic physostigmine, it gets into the CNS
treat direct acting muscarinic agonist poisoning with
atropine (also organophosphate poisoning)
