Cholinergic Antagonists Flashcards
What is an agonist?
Molecule found in nature/made in lab
binds to specific receptor –> elicit same response as endogenous compound would when bound
What is an antagonist?
Molecule found in nature/made in lab
incompletely binds to specific receptor
blocks usual response from occurring
can also observe opposite response –> dry mouth instead of salivation
Can the dose amount of agonist/antagonist alter observed effects? If so why?
Yes
higher doses can engage in more receptors or more receptor types –> exaggerated response + signs of toxicity (more pathways triggered)
What are the 2 types of Cholinergic antagonists?
Muscarinic Antagonists
Nicotinic Antagonists
What is another name for a cholinergic antagonist?
Anticholinergic
What is another name for a muscarinic antagonist?
parasympatholytic
antimuscarinic
What does a muscarinic antagonist do?
Block effects of parasympathetic autonomic discharge
What are 2 examples of muscarinic antagonists?
Atropine
Scopolamine
What are the 2 types of nicotinic antagonists and what do they do?
Ganglionic Blockers - block ALL outflow past ganglionic level
Neuromuscular Blockers - prevent skeletal muscles from working properly
What are some examples of Nicotinic Antagonists?
Tetraethylammonium
Tubocurarine
Succinylcholine
What is another name for Atropine?
Hyoscyamine
Where does atropine come from?
Origianally isolated from plants –> Atropa belladonna
Derivatives synthesized in lab
What is atropine?
classic cholinergic antagonist
What are some other drugs that have similar structures and produce similar effects as Atropine?
Antihistamines
Phenothiazine antipsychotics
Tricyclic antidepressants
What are the actions of atropine?
Resversible block muscarinic receptors –> prevents ACh from binding to those sites
Will Atropine block actions of exogenously administered cholinergics or endogenous acetylcholine?
Typically blocks actions of EXOGENOUSLY administered cholinergics
Which tissues are most sensitive to Atropine?
Salivary
Bronchial
Sweat glands
What other tissues are effected by Atropine?
Eye
CV system
GI tract
GU tract
CNS
What are the CNS effects of anticholinergics and why do they produce those effects?
Atropine –> minimal CNS effect; can’t cross BBB
Scapolamine –> drowsiness/amnesia; can cross BBB
What are some signs of scopolamine toxicity?
CNS excitement
CNS agitation
hallucinations
coma
Which antimuscarinic is used in Parkinson’s and what is it treating?
Benztropine
treat tremors
Why would you use antimuscarinics to treat Parkinson’s?
In parkinson’s there is to much ACh
Benztropine will block ACh effects
How would you treat motion sickness and how would you administer the drug?
Scopolamine patches
Injection, orally, transdermal patch
What are the effects of Antimuscarinics on the Eye?
block cholinergic stimulation of pupillary constrictor muscle –> mydriasis (unopposed sympathetic dilation)
prevent contraction of ciliary muscle –> cycloplegia (loss of accommodation) –> unfocused near vision –> blurry vision
Reduce lacrimal secretion –> dry eye
can DANGEROUSLY worsen narrow angle glaucoma (lack of outflow of aqueous humor)
What are the therapeutic uses of antimuscarnics on the eye?
used for opthamologists to view the retina –> mydriasis and cycloplegia = good in this case
But not commonly used anymore
How are antimuscarnics administered in the eye?
Drops
Ointment
What are the low does effects of antimuscarinics ( .5 mg atropine) on the cardiovascular system?
atropine block M1 receptors only –> bradychardia; ACh still can bind to M3
What are the effects of moderate to high doses of antimuscarinics (1-5 mg atropine) on the cardiovascular system?
block M2 receptors in SA/AV nodes that USUALLY slow HR –> tachycardia
like inhibiting brakes on HR
What are the effects of toxic doses of antimuscarinics (>10 mg atropine) on the cardiovascular system?
intraventricular condition block –> inhibits electrical pulse generation in pacemaker nodes
Why does antimuscarinics (atropine) have little effect on BP?
There are minimal innervations from parasympathetic system
What are the therapeutic uses of antimuscarinics (atropine) in CV disorders?
During acute MI or SA/AV node function –> bradycardia; so you want to give moderate dose of antimuscarinic (atropine) –> block M2 receptors –> increase HR