Cholinoceptor anantagonists Flashcards
Definition of affinity
The strength with which an agonist binds to a receptor
Definition of efficacy
Once the drug is bound to its receptor, the ability to transduce a response and activate intracellular signalling pathways
Definition of a competitive antagonist
Binds to the receptor for a few milliseconds, the response is surmountable, with enough agonist the effect can be overcome
What is ‘use-dependent’ block?
These drugs work by blocking the ion channel so the more agonist present means that more ion channels are open and so there is more opportunity for the antagonist to block it. They result in incomplete block; do not switch it off but slow it down significantly
What is competitive receptor antagonism?
This is when the effect of the antagonist can be overcome by increasing the concentration of agonist
Why may a nicotinic cholinoceptor antagonist be given?
In case of high BP, as a hypotensive. It works as it stops SNS innervation to blood vessels of vasoconstriction.
When might Trimetaphan be needed
Short-acting hypotension in surgery
What is alpha bungarotoxin an example of?
Receptor blockade antagonist; binds covalently to prevent ion channel opening. This is irreversible and there is a total loss of autonomic function. It causes paralysis of the skeletal muscle and diaphragm.
what are the effects of atropine and hyoscine at low and high doses?
Atropine: low dose has no effect. Mild restlessness and agitation at toxic dose
Hyoscine: sedative at low dose. CNS depression or paradoxical CNS excitation + pain
Use of tropicamide
Used in examination of the retina, it causes pupil dilation (mydriasis)
Explain the clinical use of muscarinic receptor antagonists in surgery
Used as an anaesthetic premedication; blocks constriction of trachea and bronchioles. Blocks production of copies, watery secretions from salivary glands (stops build up of fluid in lungs). Protects the heart rate as the anaesthetic is already decreasing HR so by inhibiting PNS innervation to the heart it will counterbalance this. Also, hyoscine has a sedative effect
What are hyoscine patches for and how do they work?
Motion sickness
They work by blocking the cholinergic relay of information from the vomiting centre due to sensory mismatch of the brain having received info from the labyrinth of the inner ear (about posture)
What is the use of muscarinic receptor antagonist in Parkinson’s
In PD there is loss of the neurostrial dopaminergic neurones which release dopamine-control fine movement. The normal PNS cholinergic effect is to act on the D1 receptor and reduce its activation. The antagonist will block the M4 receptor acting on the D1 receptor -therefore blocking cholinergic inhibition of dopamine release
What is pralidoxime used in
Used in anti cholinesterase poisoning
What are the unwanted muscarinic receptor antagonist side effects
Decreased sweating, Decreased secretions, Cylopegia (accommodation ability of ciliary muscle), CNS dysfunction
