Antagonists Flashcards Preview

PM2C: Therapeutics and Patient Care: Autumn > Antagonists > Flashcards

Flashcards in Antagonists Deck (10):

Describe what an antagonist is?

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


What does IC50 mean and what does it mean?

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


How do you measure antagonist action?

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


What is the dose ratio?

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


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

Increases it


What does a dose ratio of two represent?

Twice as much agonist is required to cause the same response


What does the Schild plot show?

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


What does KB represent?

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


What does -LogKb (pKb) represent?

- 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



What does insurmountable antagonism mean?

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