Receptor theory 3 Flashcards
What are some mechanisms of drug antagonism?
Antagonism by receptor block, non-competitive antagonism, chemical antagonism, pharmacokinetic antagonism and physiological antagonism.
What are the features of reversible competitive antagonism?
There is a parallel shift in response curve and no reduction in maximal response.
What is the mechanism behind reversible competitive antagonism?
The antagonist rate of dissociation is high and an equilibrium is rapidly established with the addition of an agonist. The agonist can therefore displace the antagonist from the receptor
What are the features of irreversible competitive antagonism?
Antagonists dissociate very slowly from the receptor and there is no change in antagonism occupancy when the agonist is applied.
When does irreversible competitive antagonism occur?
It occurs with drugs with reactive groups that form covalent bonds with the receptor, such as omeprazole, aspirin and monoamine oxidase inhibitors.
What are the features of non-competitive antagonism?
The antagonism blocks the chain of events that leads to the evoked response.
What is an example of non-competitive antagonism?
Verapamil and nifedipine prevent calcium ion influx through cell membranes, producing a non-specific block of smooth muscle contraction induced by other drugs, such as ACh.
What is chemical antagonism?
When two drugs combine in solution so that the effect of the active drug is lost.
What is an example of chemical antagonism?
Chelating drugs binding to heavy metals, neutralising antibodies vs. protein mediators (cytokines).
What is pharmacokinetic antagonism?
Where one drug reduces the concentration of an active drug at its site of action.
What are the mechanisms pharmacokinetic antagonism can act through?
Change in rate metabolism, change in absorption, change in renal excretion.
What is physiological antagonism?
The interaction of two drugs whose opposing actions cancel each other.
What is an example of physiological antagonism?
ACh vs. Na on heart rate, histamine-induced acid secretion vs omeprazole inhibition of proton pump.
What is the dose ratio?
The ratio by which the agonist concentration is increased in the presence of the antagonist to restore the given response.
What is a Schild plot?
Antagonist conc. against log (DR-1).
