PHARM - Pharmacodynamics - Week 2 Flashcards
Define drug potency. What tow factors is it not concerned with?
It is how much drug is needed for an effect, and not the binding (affinity) or the size of the response (efficacy).
What gives an indication of drug selectivity?
Relative affinity for different receptors.
What is the effect of α-adrenoreceptors on the following:
Blood vessels
Pupils
GIT
Nerves
Blood vessels - constriction
Pupils - dilation
GIT - constriction
Nerves - inhibited transmitter release
What is the effect of β-adrenoreceptors on the following:
Heart
Kidney
Skeletal blood vessels
Bronchi
Heart - increased rate and force
Kidney - renin secretion
Skeletal blood vessels - dilate
Bronchi - dilate
Describe a partial agonist.
It is an agonist that only provides a partial maximal response compared to a full agonist. On a response-dose curve, it looks like a full agonist response, but compressed downwards.
How do partial and full agonists differ when it comes to the number of receptors that need to be occupied to elicit the maximal response?
Partial - all receptors must be occupied for a maximum response.
Full - not all receptors need to be occupied for a maximum response.
Do partial agonists have a receptor reserve? What about full agonists?
Partial agonists have no reserve. Full agonists do.
Can a response be affected by changing the receptor number?
Yes.
What three factors is potency dependent on (7)?
Drug properties
-ability to bind (affinity)
-ability to activate (efficacy)
Tissue properties
-receptor density
-efficiency of stimulus-response coupling
Pharmacokinetics
Define competitive antagonism.
Agonist and antagonist compete for the same site on the receptor. Only one can bind at a time. One bound drug prevents the other from binding.
Consider a response-dose curve. What effect does competitive antagonism have on it?
Parallel, rightward shift, with an unchanging maximum.
The potency decreases, meaning more agonist is needed for the same response.
Consider an insurmountable antagonist. Describe what happens to a response-dose curve in this case. List three kinds of antagonists in which this kind of effect is seen.
The maximum is depressed, with a rightward shift that is not parallel.
It is seen with competitve antagonists that are slowly reversible or irreversible, and with non-competitive inhibitors.
Describe 4 instances of non-competitive interactions.
Chemical antagonism to the drug - another drug or antibodies
Allosteric modulation - binding to a different site on the target
Pathway inhibition - multiple targets within the activation/stimulus response
Functional antagonism - two agonists with opposite effects
Give an example of functional antagonism.
Noradrenaline which increases heart rate as part of the sympathetic pathway
Acetylcholine which decreases heart rate as part of the parasympathetic pathway
Is allosteric modulation always inhibitory?
No
