Antagonism-comp, non comp, irreversible Flashcards
(32 cards)
What is an antagonist?
A ligand that binds to a receptor without causing a biological effect, but blocks the action of an agonist.
What are the properties of an antagonist?
Has affinity for the receptor but no efficacy; it blocks but does not activate.
What are the four main types of antagonism?
Competitive, Non-competitive, Irreversible Competitive, and Uncompetitive.
What is competitive antagonism?
Reversible binding to the same site as agonist; can be overcome by increasing agonist concentration.
What is non-competitive antagonism?
Binds to an allosteric site, altering receptor conformation; cannot be overcome by more agonist.
What is irreversible competitive antagonism?
Binds covalently to the active site, permanently blocking receptor function.
What is uncompetitive antagonism?
Requires receptor activation by an agonist before it can bind to a separate allosteric site.
What happens to Emax and EC50 with competitive antagonists?
Emax stays the same, EC50 increases (right shift in dose-response curve).
How can you reverse competitive antagonism?
By increasing the concentration of the agonist.
What is an example of a competitive antagonist?
Naloxone at opioid receptors.
What is the equation used to calculate receptor occupancy with a competitive antagonist?
[DR]/[RT] = [D] / (Kd(1 + [B]/Kb) + [D])
What happens to Emax with irreversible antagonists?
Emax decreases due to permanent receptor inactivation.
Can irreversible competitive antagonism be reversed?
No, not by increasing agonist; new receptors must be synthesized.
Where does a non-competitive antagonist bind?
To an allosteric site, not the active (agonist) site.
What is the effect of non-competitive antagonism on Emax and EC50?
Emax decreases, EC50 typically unchanged.
Can non-competitive antagonism be reversed by increasing agonist?
No, the effect cannot be reversed by more agonist.
What are examples of non-competitive antagonists?
Rilpivirine (HIV), Allopurinol (gout).
How does uncompetitive antagonism work?
It binds only after the receptor is activated by an agonist.
What is a key feature of uncompetitive antagonists?
Higher agonist concentrations improve antagonist binding.
What is an example of an uncompetitive antagonist?
Memantine (used for Alzheimer’s disease).
What is physiological antagonism?
Two drugs produce opposite physiological effects via different pathways.
What is chemical antagonism?
A drug reduces the concentration of an agonist through chemical interaction (e.g., infliximab).
What is pharmacokinetic antagonism?
A drug alters the ADME of another drug, reducing its effect.
How do competitive antagonists affect the dose-response curve?
Shift it to the right without changing Emax.
