Study sets, textbooks, questions
Upgrade to remove ads
Agonists and antagonists
Terms in this set (18)
Wat is affinity?
is how avidly the drug binds to its receptor, how well the key fits in the lock
wat is intrinsic activity?
is efficacy, a measure of the magnitude of the effect that the drug produces after it has bound to the receptor
wat is potency?
potency is a measure of the quantity of a drug needed in order to produce the maximal effect. If a large dose isrequired to produce max effect a drug is not very potent. If a small dose produces the maximal effect a drug is considered to be potent
How can we compare potency of 2 drugs?
by using either the median effective concentration (EC50) or the median effective dose (ED50)
Describe what you mean by the terms EC50 and ED50
EC50 is medain effective concentration, is the concentration of a drug that produces a specific response that is exactly half way between baseline and maximum
Ed50 is median effective dose, is the dose of a drug that induces a specific response in exactly 50% of the population who take it.
What is an agonist?
is a drug that has significant affinity for its receptor and has full intrinsic activity. Therefore when it binds to the receptor it produces a maximum response that the receptor is capable of mediating, this is described as having an intrinsic activity of 1.
What is a partial agonist?
a drug that has significant receptor affinity but only partial intrinsic activity. So unklike with a true agonist, when the drug binds to the receptor a maximum response is never mediated despite and increase in the dose of the durg. It is therefroe said to have an intrisic activity of between 0 and 1. Example is buprenorphine acting at the mu-receptor.
Partial agonists can act as either agonists or antagonists, depending on the circumstances. If used alone they are agonists because they produce a response, even if it is not the mscimu response that a true agonist would prodcue. They als oact as agonists if they are used alongside a low dose of a true agonist. However, if they are used in conjunction with high doses of a true agonist for the same receptor, the partial agonist will act as a competitive antagonist. This is because they will compete with the true agonist for the receptro, preventing the true agonist from having full occupancey and therefore preventing max response.
So the distinguishing feature of a partial agnoist is that it fails to produce a maximal effect even at very high doses when all receptors are occupied.
What is an inverse agonist?
a drug that has significant receptor affinity and intrinsic activity, but it exerts an opposite effect to the endogenous agonist.
what is an antagonist?
has significant receptor affinity, but has no intrinsic activity. So when a drug binds to the receptor no response is mediated. Theyr are therefor described as having an intrinsic activity of 0.
What different types of antagonists do you know about?
They can be classified as irreversible and reversible. Reversible can be further classified into competitive and non-competitive.
Reversible competitive antagonists compete for the same receptor as the agonist, this means that the effect of the antagonist can be overcome by increasing the dose of the agonist. Examples of competitive antagonists include the non-depolarising muscle relaxants which compete for the nicotinic receptor on the NMJ and beta blockers wihc compete with adrenaline at the beta adrenergic receptor sites in the heart.
Reversible non-competitive antagonists prevent receptor activitation through conformational distortion of the receptor rather than binding to the same site as the agonist or altering binding of the agonist. Because they are non competitie their action cannot be overcome by incerasing the concentration of the agonist. An example is ketamine, which atangonises glutamate at the NMDA receptor.
Irreversibele antagonist bind irreversibly to the receptor or at a distant site and prevent the agonist from binding to its recepotr. Increasing the dose of the agonist will not overcome the clockade because the antagonists has bound irreversibly. Example is phenoxybenzamine, which binds irreversibly to alfa adrenoceptor antagonizing the effect of catecholamines.
What is the difference between a competitive atntagonist and an inverse agonist?
an inverse agonist will exert its own physiological effect, the opposite to the endogenous agonist. A competitive antagonist has no direct effect of its own and simply stops the endogenous agonist exerting its effect.
wat is de dose-response curve?
it is a graph with the concentration fo the drug on the x axis and the response on the y-axis. it is hyperbolic in shape. It shows taht initially as the drug concentration incerases and the receptor occupancy increases, so accordingly the reponse increases dramatically. However, when the number of empty receptors decreases, the effect of increasing the durg dose has a samller effect on the reponse elicited, so the slope of the curve flattens out completeley at 100%.
Zie plaatje op pag 161.
Dus drug concentration in mg/ml op x as, en percentage of maximum response op y-as.
What is a log-dose response curve? What is its advantage?
is a semi-logarithmic plot. The curve is plotted using a logarithmic scale for the dose on the x axis and the response on the y axis.
Unlike the hyperbolic shape of the dose resopnse curve this produces a sigmoid shape curve. The hyperbolic shape makes it difficult to identiy the maximum response and also makes it hard to make comparisons with other agonists and antagonist. When using the log0dose reponse curve, the steep part of the curve is apporximately linear. this makes the assessment of the relationship between dose and response easier to understand. The ED50 is on the steep, linear part of this curve.
zie afbeelding c pag 161
How would the curve for a drug with a lower potency compare to a drug with a higher potency?
The potencey of the drug will cause a parallel shift of the curve to the left or the right .A more potent drug will shift the curve to the left, because lower concentrations are required to produce the response. A drug with less potency will move the curve to the right, as higher concentration is required to produce the same response. The mascimum response of both of the drugs will e the same, so the height of the curves is identical
What else would make the dose reponse curve move right, except lower potency.
If a competitive antagonist is given alongside a full agnost, this will also cause a parallel shift of the curve to the right. This is because a higher concnetraiton of the agonist is then required to produce the full reponse because it's competing with the antagonist.
What would happen to the shape of a dose reponse curve if a non-competitive antagonist was given?
the log dose curve will again move to the right, however in addition, the maximum achievable response is reduced. This is because when a non-competitve antagonist is given, even increasing the dose of the agonist will not overcome the effects of the antagonist. Therefore the maximum response can never be achieved. zie figuur op pag 162
What would happen to the shape of a dose response curve if the drug was a partial agonist?
If a partial agnoist is given there is no parallel shift in the curve, however it will be impossible to elicit the masx response despite high drug dose, so the hight of the curve would be smaller.
Zie figuur e op pag 163
What is the dose ratio?
Is the term used to describe the extent of the rightward shift of the log-dose response curve in the presence of a competitive antagonist. It is used to determine the ffactor by which the dose of the agonist must be increased to produce a maximal response in the presence of the competitive antagonist.
Dose ratio=dose of agonist in presence of inhibitor/dose of agonist in absence of inhibitor.
Sets found in the same folder
Measurement of xygen, carbon dioxide and anaesthet…
Drugs acting on the gastrointestinal tract-3
Measurement of oxygen, carbon dioxide and anaesthe…
Other sets by this creator
Drugs actin on the central nervous system-2
Drugs acting on the central nervous system-1
Drugs acting on the gastrointestinal tract-2
Recommended textbook solutions
Clinical Reasoning Cases in Nursing
Julie S Snyder, Mariann M Harding
The Human Body in Health and Disease
Gary A. Thibodeau, Kevin T. Patton
Mecânica dos Materiais
Barry J. Goodno, James M. Gere
Principles and Foundations of Health Promotion and Education
Denise Seabert, James McKenzie
Other Quizlet sets
CMT Guide Questions
CSCI101: Exam 2
ACTG 6100 exam 1_ chapter 6
RED CH. 6 & 7