7: Cholinoceptor Antagonists

Question 1

Define competitive antagonist

Answer 1

except it doesn’t induce a response. Increasing the concentration of the antagonist = increases likelihood of the antagonist binding to a receptor (as opposed to agonist binding)

Question 2

Interefering w nicotinic cholinoceptors can affect which part of ANS

Answer 2

PS + S depending on which is dominant

Question 3

How can nicotinic receptors act

Answer 3

• blocking the nicotinic receptors and so prevents ACh from interacting - the drug has affinity to the receptor
• Block the ion channel itself thus they’re called ‘ion channel blockers’. They get into the ion channel and prevent the ions from passing through. If the majority of the action is through ion channel blockade, then the affinity is irrelevant- it is a physical blockade of the receptor.

Question 4

Define use-dependent block

Answer 4

term referring to the fact that these drugs work most effectively when ion channels are open.

Question 5

Sympathetically dominated tissues include + effect of nicotnic receptor antagonists:

Answer 5

Kidneys (increase renin secretion, Na and H2O reabsorption) + Blood vessels (particularly vasoconstriction in the gut).

Showsa hypotensive effect. The BP falls because these sympathetically driven responses in the kidneys and blood vessels to increase BP are reduced.

Question 6

PS dominated tissues include:

Answer 6

Eyes, lungs, bladder, ureters, GIT, exocrine secretions

Question 7

Effects of nicotinic receptor antagonists on eyes

Answer 7

• Parasympathetic action acts to maintain a level of partial pupil constriction at rest. This allows them to dilate or constrict further when necessary. Administering ganglion blocking drugs will hence cause pupils to dilate.

Question 8

Effects of nicotinic receptor antagonists on lungs

Answer 8

. The bronchioles are always partially constricted under parasympathetic control so that further dilation or constriction can occur when required. These drugs tend to cause bronchodilation when the parasympathetic effect is lost.

Question 9

Effects of nicotinic receptor antagonists on bladder, ureter, GIT

Answer 9

Bladder dysfunction, loss of GI motility, tone and secretions

Question 10

Effects of nicotinic receptor antagonists on exocrine secretions

Answer 10

Reduced secretions overall. S driven sweating will decrease so ability to thermoregulate is affected

Question 11

Hexamethonium action

Answer 11

Ion channel blockage mechanism is predominant.

First anti-hypertensive drug but many side effects

Question 12

Trimetaphan

Answer 12

predominant mechanism is receptor antagonism.

Given when pt needs hypotensive during surgery/ given in specific situations

Question 13

How does alpha-bungarotoxin work

Answer 13

targets the skeletal muscle of the somatic NS. This causes paralysis of the skeletal muscle and diaphragm which leads to suffocation and death.

Question 14

Muscarinic receptor antagonists have effects on which part of ANS

Answer 14

PNS

Question 15

Give examples of nicotinic receptor antagonists

Answer 15

hexamethonium + trimetaphan

Question 16

Give examples of muscarinic receptor antagonists

Answer 16

atropine + hyoscine + topicamide

Question 17

Effects of high dose atropine

Answer 17

restlessness + CNS agitation

Question 18

Effects of hyoscine at normal and high dose

Answer 18

Normal: sedative and amnesia
High: CNS depression and paradoxical CNA excitation

Question 19

How do you treat motion sickness

Answer 19

Hyoscine patch blocks muscarinic receptors in vomiting centre to stop feeling nausea.

Question 20

Which, atropine/hyoscine, penetrates brain better?

Answer 20

hyoscine - more lipid soluble

Question 21

Topicamide uses

Answer 21

a muscarinic receptor antagonist for the eye. The PNS causes iris constriction which then causes the pupil to get smaller. With the use of an antagonist, the pupil will dilate instead.
This is used in eye exams to examine the retina.

Question 22

Uses of muscarinic receptor antagonists

Answer 22

COPD + Asthma
Parkinsons
Anaesthetic premedication

Question 23

What is ipratropium bromide

Answer 23

Muscarinic receptor antagonist - easier to trap in the lungs when inhaling. It is quite difficult for this drug to cross membranes. The drug has its blocking effect on the muscarinic receptors in the airways and due to its polar molecule attached, it cannot cross through into the blood so it doesn’t have a muscarinic side effects. It’s chosen over atropine bc of quaternary N – v polar.

Question 24

Muscarinic receptor antagonist unwanted effects

Answer 24

• Hot as Hell Causes decrease in sweating and loss of thermoregulation
• Dry as a bone Reduced secretions (PNS regulates these)
• Blind as a bat Ability to focus on near objects is PNS driven so if the muscarinic receptors are blocked, the ability to focus is lost (Cyclopegia)
• Mad as a hatter CNS disturbance

Question 25

Which medication used to treat atropine poisioning

Answer 25

Physostigmine - blocks acetylcholinesterases. Increase in ACh in synapse outcompetes atropine

Question 26

How does botulinum toxin work

Answer 26

Prevents ACh from being exocytosed and getting to the synapse. It interferes with the SNARE complex. Botulinum prevents the vesicles docking with the membrane and then getting out. It is very dangerous toxin and potent