3. Pharmacodynamics 2 Flashcards
Define “affinity”.
Affinity is the strength at which a ligand binds to a receptor and form a stable complex.
What is a measure of affinity?
Kd = equilibrium dissociation constant
What is the equilibrium dissociation constant (Kd)?
The concentration of an agonist at which 50% of the available receptors in the system have been bound, to form agonist-receptor complexes.
What is the relationship between equilibrium dissociation constant (Kd) and affinity?
The lower the Kd, the higher the affinity.
Define “efficacy”.
Efficacy is the ability of the ligand, once bound, to activate a receptor to produce a biological response.
How is efficacy measured?
Using maximum efficacy (Emax).
What are the two types of agonist distinguished by efficacy?
- Full agonist
- Partial agonist
Define “full agonist”.
A full agonist is an agonist that is able to produce a maximal response, while only occupying a small % of the receptors available. They have high efficacy (high Emax).
Define “partial agonist”.
A partial agonist is an agonist that is unable to produce a maximal response, even when all the agonists have bound to all available receptors in the system. They have lower efficacy (lower Emax).
Define “agonist”.
An agonist is a ligand that binds to a receptor to produce a cellular response.
Define “potency”.
Potency is the amount/concentration of a drug/agonist that is required to give a certain level of effect (e.g. 50% of maximum efficiency).
What is a measure of potency?
EC50 = concentration of a ligand where a 50% of the maximum efficacy is observed (not always at 50%, if maximum efficacy is 80%, then the level to look at is 40%).
What does potency depend on?
- Affinity of drug
- Efficacy of drug
- The number of receptors
- Efficiency of the stimulus-response mechanisms
