Cholinergic Receptor Anatgonist3 Flashcards
What are the physiological effects of atropine on the cardiovascular system?
the effects of atropine on heart are complex;
1) low dose produce a paradoxical bradycardia which may be due to blockade of M1 autoreceptors which would result in increased ACh release
2) higher doses blockade of the M2 receptors of the heart occurs, leading to tachycardia–the rate of AV conduction is elevated
3) atropine alone has no effect on the circulation but, it will reverse the vasodilation produced by cholinergic agonist
What happens when doses of atropine are high enough to decrease gastric acid secreation and dilate the brochoni?
it will also affect all other structure under muscarinc control. as a resul atropine and most other muscarinic antagonist are not very desirable for treating peptic ulcer disease or asthma
What are the contraindications of atropine?
1) men with prostatic hypertrophy
2) closed angle glaucoma
3) cardiac disease
4) myasthenia gravis
5) GI obstruction
6) intestinal colitis and atony
What can happen with VERY high dose of atropine?
remember pharse: dry as a bone, blind as a bat, red as a beet, and mad at as hatter
@ very high doses—-> coma and death occur
What are the side effects of atropine comparing adult to children?
adults okay w/ large doeses of atropine—> treat symptoms (keep cool)
dangerous in children—> uses a little physostigmine (reverse block)
What are the side effects of atropine>?
affects organ system just described. The most obvious effects are:
The DUCT:
d-dry mouth
u-urinary retention
c-constipation
t-tachycardia—M2 blockade
in addition, pronounced sedation can occur due to CNS action
What are the physiological effects of atropine on the glands?
atropine blocks ACh—> stops sweating—> body temp goes up (bad for babies and kids)
What are the physiolgocial effects of atropine on the gi tract?
1) atropine stops ACh—-> GI tone and motility lowers (not completely stopped b/c NANC-non adrenergic non cholinergic release from enteric nervous system)
2) atropine lowers:: acid secretion, proteolytic enzymes, and mucin (H2 now replaced anti-muscarinics like atropine)
What are the physiolgocial effects of atropine on the respiratory system?
bronchodilation and reduction of secretions occur
more pronounced effects are observed in patients with asthma and chronic obstructive pulmonary disease; atropine will also prevent secretions and laryngospasm produced by inhalation anesthetics
What happens during an overdose with atropine?
overdose of atropine—-> blocks PSNS function—> 1. derilium 2. agitation 3. higher body temperature 4. flushed skin
Name the drug interactions of atropine?
1) drugs w/ anti-muscarinic effects ( tricyclic anti-depressants, antipsychotic, histamine H1 blockers)
2) CNS depressants- potentiate depression
3) MAO inhibitors- more side effects of MAOI b/c unopposed sympathetics activity
What are the physiological effects of atropine on the CNS?
at therapeutic it causes mild stimulation of the PSNS medullary centers (which may cause bradycardia) and mild sedation
at high doses excitement, agitation, hallucinations and coma may result
What is another name for atropine. Hint there are 5
1) atronet
2) atropa
3) atrosun
4) tropine
5) bellpino-atrin
What are the therapeutic uses of atropine? Hint 9 uses!
1) treat irritable bowel syndrome that fails to respond to other treatments
2) decrease gastric motility and acid secretion in conjunction w/ H2 blockers for ulcers
3) treat spastic disorders of GI and genitourinary tract
4) trat urinary incontinence and enuresis by increasing bladder capacity and reducing tone
5) decrease salivation for inhalation anesthetics
6) prevent reflex bradycardia and hypotension during surgery
7) emergency treatment of severe bradycardia
8) reverse ACh-esterase inhibitor toxicity
9) parkinsonism
What order does atropine impact and what happens salivary glands, sweat glands, bronchial glands, heart, eye, urinary tract, intestine, lung and stomach?
low to high:
salivary, sweat, and bronchial glands
heart—> eye
urinary tract—-> intestine—> lung—-> stomach
What does atropine do and how does it impact receptors..which receptors?
its a competitive antagonist at muscarinic receptors; affinity for the different muscarinic receptors are similar
Where does atropine come from and what is its use?
derived from the deadly nightshade plant–atropa belladonna; atropine has been used as poison and cosmetically dilate pupils
What is important to know about the structure of atropine?
its a tertiary amine, thus it is widely distributed and enters the CNS
How is atropine an important about how atropine is removed from the body?
its rapidly eliminated in adults but not children
What are the physiological effects of atropine on the eye and how long does it last ?
local application prevents the action of ACh on the iris sphincter muscle and ciliary muscle (effect last 7-10 days)
Physiological effects:
result in pupillary dilation (mydriasis) and paralysis of accommodation (photophobia)—-> pupillary response to light is lost
eye will focuses on far vision, near objects may appear blurred and smaller than they are due to the paralysis of accommodation
***those patients with closed angle glaucoma may have dangerous increase in intraocular pressure but with systemic atropine: little ocular effects***
What is the connection between atropine at different levels of doses?
at low doses:
salivary glands, sweat glands, bronchial glands
at intermediate doses:
heart rate increase, eyes mydriasis, blurred vision
at high doses:
urinary tract- interference w/ voiding
intestine-decreased tone and motility
lung-dilation of bronchi
at very high doses:
stomach-decreases acid secretion: note that doses of atropine that are high enough to decrease gastric acid secretion or dilate the bronchi will also affect all other structers under muscarinic control; as a result, atropine and muscarinic
as a result atropine and most other muscarinic antagonists are not very desirable for treating peptic ulcer disease or asthma
Describe the schematic diagram of the interaction of drugs with acetylcholine receptors on the endplate channel.
For non-depolarizing blocker.
for drugs such as tubocurarine–preventing the opening of the channel when it binds to the receptor
Describe the schematic diagram of the interactions of drugs with the acetylcholine receptor on the endplate channel.
A depolarizing blocker
for example a succinylcholine, both occupy the receptor and blocking the channel; normal closure of the channel gate is prevented; depolarizing blockers may “desensitive” the endplate by occupying the receptor and causing persistent depolarization
Where is the site of action of ganglionic blockers?
- nicotinic receptors in the sympathetic & parasympathic ganglion
- receptor on the adrenal medulla
Give an example of why understanding the predominant tone is important in predicting how the ganglionic blocker impacts an organ.
the heart has both PSNS and SNS innervation;
PSNS (slows heart) is the predominant innervation; ganglionic blocker reduce both type of innervation. PSNS will be affected the most and net effect will be SNS predominance leading to tachycardia.
What the predominate tone of arterioles?
sympathetic (adrenergic)
How do ganglionic blockers work?
they do not cuase depolarization-block transmission without intial stimulation
What the first ganglionic blockers?
- tetraethylammonium and hexamethonium (blocked ganglionic nicotinic receptors)
What is trimethaphan and what is its commerical name?
- ganglionic blockers
- arfonad is the commerical name
Give an example of two synthetic amines and what are their properties?
1) mecamylamine is a synthetic amine; its a teritary amine and can be ionized or unionized depending on the pH (alkalinzation favors the unionized form); its administered orally and can cross the BBB
2) trimethaphan is another and it is a charged S+ compound; it is administered parenterally; it does not enter the CNS
How can AChE inhibitors help deal with non-depolarizing blockers/ competitive surmountable antagonist?
AChE inhibitors will surmount the block; if channel block has occured AChE inhibitors will be less effective
How can apena be caused other than genetic defects?
rapid potassium release may contribute to apnea in patients with electrolyte imbalances
How does long succinylcholine duration of action last?
very brief duration of action in blood-quickly metabolized by pseudocholinesterase–only a small fraction of drug reaches NMJ
How does non-depolarizing neuromuscular blockers impact the CNS?
positively charged-poor lipid soluble–do not enter CNS
How does succinylcholine impact the nicotinic receptors?
produce similar action as ACh but the duration of action is longer than ACh; the longer duration of action allows it to act as a blocker
How fast are non-depolarizing neuromuscular blockers excreted?
they are rapidly excreted
How is succinylcholine metabolized at the NMJ and how does that impact nicotinic receptors ?
its not metabolized by true AChE-drug has to diffuse from synapse to be metabolized; thus succinylcholine at the NMJ can interact with nicotinic receptors for a long period of time; nicotinic receptors will become desensitized because of this reason
How long do the actions of cyclopentolate and tropicaimide last?
its used more than atropine since effects are shorter in duration: 0.25 to 1 day vs. 7 days
Where is the site action of neuromuscular blockers?
the nicotinic receptors on the striated muscle—site of action of neuromuscular blockers
What are the uses of ipratopium bromide and tiotropium?
1) bronchitis
2) emphysema
3) chronic obstructive pulmonary disease (COPD)
4) with beta-2 receptor agonist for asthma
What is the volume of distribution for non-depolarizing neuromusular blockers?
the volume od distribution is about equal to the blood volume
what other medical procedures does neuromuscular blockers assist with?
- orthopedic procedures
- intubation
which patients should be cautions in taking neuromuscular blockers patients?
- heart failure patients receiving digitalis or diuretics
- soft tissue damage
- ocular laceration
- muscle dystrophies
How do non-depolarizing blockers- competitive (surmountable) antagonist impact Na+ channels?
- block prejunctional Na+ channels- (top) prevent ACh release
What is tubocararine?
- prototype agent
- non-depolarizing neuromuscular blocker
What is tiotropium and what is another name for it?
- Spiriva
- quaternary amine dervative of atropine
How are non-depolarizing neuromuscular blockers administered?
not orally bioavailable; all are given IV
Where is the site of action of antimuscarinic drugs?
- effector organs in the parasympathetic pathway
What is tropicamide?
- antimuscarinic agent
Why have synthetic antimuscarinic drugs declined in usage?
many have been developed but their use has declined due to the discovery of more selective agents and the pronounced side effects associated with these drugs