L4 - principles of drug action Flashcards
what shape is the graph of proportion of drug receptors occupied against drug concentration
rectangular hyperbola
what shape is the graph of receptors occupied against log drug concentration
symmetrical sigmoid
what is the KD
the molar concentration of drug required to occupy 50% of the receptors at equilibrium.
the lower the KD the higher the affinity of the drug.
equation for rate of forwards and backwards reaction at a receptor
forward = K+1[D][R]
backwards = k-1[DR]
where “D” and “R” are drug and receptor and “K+1” and “K-1” are rate constants that tell us the likelihood of the forwards and backwards reactions occurring.
equation for KD including “D”, “R”,”K+1”and “K-1”
KD = K-1/K+1 = [D][R]/[DR]
what does KD measure
measure of how tightly the receptor holds on the drug once they come together.
they have a slow dissociation rate (K-1 very small)
what are agonists
bind to the receptor and then ‘activate’ it. after binding, agonists produce a conformational change that will lead to a respons.
what is efficacy
the ability of a drug to activate the receptor
how many amino acids does β2 adrenoreceptor have
around 400
what are partial and full agonists
full - high efficacy (produce maximum response before activating all receptors)
partial - low efficacy (fail to produce maximum response after activating all receptors)
what is the difference between EC50 and KD
the KD only tells us about the affinity of the drug while the EC50 tells us about efficacy and affinity (overall response)
what is an antagonist
act to inhibit the effects of a neurotransmitter, hormone or in some cases another drug.
what is a chemical antagonist
use one drug to chemicals inactivate another , receptors are not involved
what is a pharmacokinetic antagonist
one drug alters the way the body deals with another, receptors not involved
what is a physiological antagonist
two drugs act to produce opposing effects and cancel each other out. in this case both drugs are agonists working at different receptors.
