Antagonists

Question 1

Describe what an antagonist is?

Answer 1

1. A drug that binds to a receptor but does not activate it and has zero efficacy
2. A drug that completely blocks out the action of the agonist
3. Doesn’t always compete with the agonist as it can inhibit the receptor action at a allosteric site
4. Has a high affinity

Question 2

What does IC50 mean and what does it mean?

Answer 2

1. The concentration of antagonist to inhibit 50% an agonist-induced response
2. Approximates affinity of antagonist for competitive reversible antagonists
3. Other analysis are better for measuring affinity IC50 usually referred to as antagonist potency

Question 3

How do you measure antagonist action?

Answer 3

By plotting a concentration response curves to an agonist in the presence of increasing antagonist concentrations

Question 4

What is the dose ratio?

Answer 4

The fold increase in agonist concentration needed to evoke a given response (normally EC50) in presence of antagonist

Question 5

What does the increase adding of an antagonist to do a dose ratio?

Answer 5

Increases it

Question 6

What does a dose ratio of two represent?

Answer 6

Twice as much agonist is required to cause the same response

Question 7

What does the Schild plot show?

Answer 7

1. Tells you if an antagonist is competitive and if so an estimate of its affinity
2. If it =1 it’s a competitive antagonist

Question 8

What does KB represent?

Answer 8

The concentration of antagonist (B) that binds to 50% of its receptors

Question 9

What does -LogKb (pKb) represent?

Answer 9

• Also known as the pA2 value
• For a competitive inhibitor, it is a measure of affinity and potency
• The concentration of the agonist to reach a dose ratio of 2

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Question 10

What does insurmountable antagonism mean?

Answer 10

In the presence of an antagonist, no matter how much agonist you add, you will never elicit a maximum response