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Flashcards in Cholinoceptor antagonists Deck (22)
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1
Q

What are the few clinically useful nicotinic receptor antagonists called and how do they block the receptor?

A

Ganglion Blockers

These block the ion channel itself (so not the receptor), thus preventing the ions from moving through the pore

2
Q

Give two examples of ganglion blocking drugs.

A

Hexamethonium

Trimethaphan

3
Q

What does ‘use-dependent block’ mean, in regards to nicotinic receptor antagonists?

A

The drugs work most effectively when the ion channels are open (i.e. when. more agonist is present at the receptor)

4
Q

What determines the effect of ganglion blockade in a tissue?

A

It depends on which limb of the autonomic nervous system (SNS or PNS) is dominant in the particular tissue (at the time e.g. at rest PNS is largely dominant)

5
Q

Which tissues are sympathetic dominated (at rest)?

A

Vasculature

Kidneys

6
Q

What is the overall effect of ganglion blockade in terms of loss of sympathetic dominance?

A
  • Decreased sympathetic-mediated vasoconstriction
  • Decreased renin secretion from kidneys (=decreased sodium and water reabsorption)

=> Hypotension

7
Q

Which tissues are parasympathetic dominated (at rest)? What effects does it have on the tissue?

A

Lungs – causes bronchoconstriction

Eyes – maintains partial pupillary constriction at rest

Bladder and ureters - contraction of detrusor; relaxation of trigone and sphincter (bladder emptying)

GI tract - increased motility and tone, increased secretions

Salivary glands - copious watery secretion

8
Q

What would the effect of ganglion blockage be on these tissues?

A
Bronchodilation 
Pupil dilation (blurred vision) 
Bladder dysfunction 
Loss of GI motility and secretions 
Decrease in exocrine secretion
9
Q

What is the clinical use of hexamethonium and trimetaphan?

A

Anti-hypertensive drug (no longer used due to the many side effects)

Hypotensive drug during surgery (short acting)

10
Q

In what types of chemicals are nicotinic receptor blockade antagonists found?

A

Toxins and venoms

11
Q

How do receptor blockade antagonists work?

A

Irreversible covalent binding to the receptor preventing the ion channels from opening

12
Q

Give an example of a nicotinic receptor blockade antagonist

A

Alpha-bungarotoxin (from common krait snake venom)

13
Q

Give four examples of muscarinic receptor antagonists

A

Atropine (plant based)
Hyoscine (plant based)
Tropicamide
Ipratropium Bromide

14
Q

What effect does atropine have on the CNS (at normal and toxic doses)?

A

NORMAL dose: little effect

TOXIC dose: Mild restlessness and Agitation (Less M1 selective)

15
Q

What effect does hyoscine have on the CNS (at normal and toxic doses)?

A

NORMAL dose: Sedation, amnesia

TOXIC dose: CNS depression or paradoxical CNS excitation (associated with pain); greater permeation into CNS than atropine

16
Q

What is tropic amide used for?

A

It is used to dilate the pupil to examine the retina

17
Q

What is an important use of muscarinic receptor antagonists with regards to surgery? Why is it useful in this circumstance?

A

Anaesthetic premedication

  • Causes dilation of airways so easier to intubate the patient
  • Causes reduced secretion (saliva + oesophageal) so none gets in airways
  • Knocks out the PNS effect in decreasing heart rate and contractility (so only anaesthetic is having thus effect)
  • Sedation (for hyoscine)
18
Q

Why is hyoscine able to treat motion sickness?

A

Muscarinic receptors are important in relaying information from the labyrinth in the inner ear to the vomiting centres.
Muscarinic receptor antagonists can reduce the flow of information from the labyrinth to the brain thus reducing the nausea.

19
Q

What degenerative disorder of the central nervous system can be treated by muscarinic receptor antagonists? Explain how.

A

Parkinson’s Disease

Muscarinic (M4) receptors have an inhibitory effect on Dopaminergic (D1) neurones. In Parkinson’s, nigro-striatal dopaminergic neurones are lost. By blocking the the M4 receptors, you allow the remaining dopaminergic neurones to fire at the maximum rate.

20
Q

Explain the use of muscarinic antagonists in treating asthma and COPD. State the specific antagonist used

A

Ipratropium Bromide

It removes the parasympathetic mediated bronchoconstriction

21
Q

Explain the role of muscarinic antagonists in treating irritable bowel syndrome. What is the specific Muscarinic receptor type?

A

Reduces smooth muscle contraction, gut motility and gut secretions

M3

22
Q

State some general unwanted side-effects of muscarinic antagonists.

A

Hot as hell - decreased sweating

Dry as a bone - decreased secretions

Blind as a bat - cycloplegia (loss of accommodation due to paralysis of ciliary muscle)

Mad as a hatter - CNS disturbance