Ch2 AGONISM, EFFICACY, AND POTENCY

Question 1

agonist

Answer 1

a drug that binds to a receptor and has the same effect as
the natural ligand

Question 2

ligand

Answer 2

something that binds to the receptor site on the target protein

Question 3

full agonist or efficacy

Answer 3

If the drug has the full/maximal effect that can possibly be elicited by a biological ligand - a full agonist has high efficacy

Question 4

partial agonist

Answer 4

If the drug can elicit only part of the effect of a natural ligand - not often used in the clinical setting

Question 5

dose-response curve

Answer 5

graphs the % of maximal biological effect against the log of drug concentration

Question 6

EC50

Answer 6

The effective concentration of a drug that provides 50% of the maximal biological effect. We use EC50 because it also tends to fall in the most linear/predictable region of a dose response curve.

Question 7

Potency

Answer 7

compares the effective concentration of a drug producing a
therapeutic effect with those of drugs that act in a similar fashion. When
two drugs have the same efficacy, the drug that has the lowest EC50 is the
more potent drug. “More potent” simply means that less drug is needed
to elicit the same effect

Question 8

Antagonists

Answer 8

bind to the same site as the endogenous ligand but do not produce the same signal as the endogenous ligand. There are two types of antagonists

Question 9

How do antagonists work?

Answer 9

they have no efficacy at that receptor, but they often have high affinity, so they can prevent the effect of another ligand

β-blockers and antihistamines are antagonists

Question 10

competitive antagonists

Answer 10

the antagonists binds to the same receptor as the natural ligand. The bonds are reversible and there is a dissociation constant k-1.

The effects of an antagonist can normally be overcome by the addition of more agonist. These competitive antagonists are very useful drugs because there is usually some kind of antidote for an overdose.

Question 11

noncompetitive antagonism

Answer 11

an antagonist that binds to a site other than the receptor the agonist binds to, and that keeps the agonist from having an effect.

This can become a problem because there is no longer competition for the receptor, and thus the antagonist cannot be “outcompeted.”

not often used clinically

“Noncompetitive” just means that the antagonist is not sitting in the same receptor as the agonist.