L4 - principles of drug action 2 - drug action at receptors Flashcards
what is a receptor
protein macromolecule in membrane (transmembrane)
2 functions of receptors
- recognition of molecule
2. transduction - bringing about effect
define affinity
how well a drug binds to a receptor
molar conc of drug required to occupy 50% of receptors at equilibrium
what does a low Kd show in relation to affinity
high affinity
low dissociation rate
define Kd
conc of drug required to occupy 50% of receptors at equilibrium
measure of how tightly receptor binds onto drug
what is equation for Kd
[products]
define agonist
something that binds to receptor and activates it
causes conformational change leading to response
define efficacy
ability of drug to activate receptor
define full agonist
an agonist that has high efficacy - can elicit max response without occupying all receptors
define partial aagonist
agonist with low efficacy
often fail to produce max effect even when all receptors occupied
does EC50 of an agonist mean 50% of receptors are occupied?
no
what is EC50 of an agonist determined by
its affinity AND efficacy
what is an antagonist
something that binds to receptor but doesn’t activate it
affinity but no efficacy
(inhibitor)
list the types of antagonism not involving receptors
- chemical
- pharmacokinetic
- physiological
what is chemical antagonism
one drug chemically inactivates another
eg poisoning
