Cholinergic Antagonists: Anticholinergics 5 Flashcards
Which cholinergic receptor is atropine selective for?
Muscarinic
What is atropine mainly used for?
Ocular and CNS applications
What is anisotropine mainly used for?
GI and PNS applications
How are muscarinic antagonist classified?
Either by tertiary amines or quaternary amines.
Of the tertiary amines, which two are alkaloids?
Atropine and scopolamine which both come from the belladonna (more attractive) plant.
They are M1,M2 and M3 non selective.
Only difference is scopolamine has an epoxide group.
What are the alkaloid tertiary amine antimuscarinics used for?
To treat GI and urinary conditions, motion sickness.
Can access CNS leading to drowsiness at low doses or hallucinations at high ones.
What do you need to know about scopolamine (Maldemar)?
Highly lipophilic due to epoxide ring.
Clinically used for motion sickness
-oral and transdermal options
SE: dry mouth, blurred vision, sedation and confusion and psychosis at high doses
What are the short acting tertiary amines?
Homatropine (less toxic) and tropicamide (short MOA)
Used in optic applications due to short action - cycloplegia and mydriasis
What are the tertiary amines used for parkinson’s disease?
Benztropine and trihexyphenidyl (high doses).
Sedative activity
Used with L-DOPA in PD patients allowing balance between dopaminergic and cholinergic neurotransmission.
What is the quaternary amine for COPD?
Ipratropium which has an additional isopropyl group compared to atropine.
M3 antagonist blocking ACh mediated construction and open the airways
Sometimes asthma and can enhance Beta adrenergic agonist in COPD.
High doses can cause Hypotension and muscle weakness.
What are the two drugs used for COPD?
Ipratropium a M3 antagonist blocking ACh related constriction and Albuterol a Beta-2-agonist. (COMBIVENT)
What is the quaternary amine for GI disorders?
Glycopyrrolate and propantheline bromide (not in US)
treat GI spasms and peptic ulcers
Glycopyrrolate can be used pre-op to reduce secretions
Charged quaternary amine keeps molecule from crossing gut.
What is the antimuscarinic drug for overactive bladder?
Tolterodine (Detrol) therapeutically acts selective to M3 receptor.
Problems: still causes typical anticholinergic effects.
NEWER options available. The -fenacin and oxybutynin.
What do neuromuscular blocking drugs look like?
very similar to acetylcholine
succinylcholine is a dimer of acetylcholine
What is the difference between a non-depolarizing blockade and depolarizing blockade?
Non-depolarizing is a normal antagonist which blocks acetylcholine from binding to the nicotinic receptor.
-tubocurarine
Depolarizing will first activate the nicotinic receptor, then block acetylcholine from binding.
What is the action of tubocuraine?
Competitive antagonist to nicotinic receptor causes non-depolarizing blockade.
Clinical: skeletal muscle relaxation during anesthesia and used for intubation
What is the action of succinylcholine?
Agonist to nicotinic receptor and causes persistent depolarization.
Muscle fibers are resistance to further simulation by ACh due to preventing the resetting of voltage gated sodium channels.
Metabolized by plasma butyrylcholinesterase (pseudocholinesterase) which is slower than AChE
Clinical: skeletal muscle relaxation during anesthesia
What are the problems with succinylcholine?
Muscle soreness, avoid hyperkalemia (high potassium)
malignant hyperthermia
prolonged paralysis due to pseudocholinesterase deficiencies (MEL)
What is the drug at indirectly blocks ACh release?
Botulinum toxin which interferes with vesicles full of ACh ready to be released into the synapse.
Clinical: dystonias which are uncontrolled muscle spasms, cerebral palsy, spasm of ocular muscles, anal fissure and excessive sweating
What is hexamethonium?
Antagonist at nicotinic receptors in autonomic ganglia blocking all SS and PS activity.
Original used was for HTN but not used anymore due to adverse effects.
What are the problems with hexamethonium?
SS
-hypotension
-decreased perspiration
PS
-Dry mouth, decreased secretions
-Tachycardia but sometimes bradycardia if SNS is active
-Mydriasis and blurred vision
-constipation
-urinary retention
