Pharmacology: Competitive and Non-Competitive Antagonists Key Concepts

What characterises competitive antagonists?

bind to the same site as the agonist, their effect can be overcome by increasing the concentration of the agonist.

Give an example of a competitive antagonist.

Atropine against ACh

What is a key feature of non-competitive antagonists?

bind to a different site on the receptor or bind irreversibly, heir block cannot be overcome by increasing the concentration of the agonist.

Provide an example of a non-competitive antagonist.

Benzilycholine mustard against ACh

How is the effect of an antagonist quantified?

comparing the effect of increasing concentrations of the agonist in the presence and absence of the antagonist.

What factors influence an antagonist's ability to block a response?

Kd of the agonist, the Ka of the antagonist for the receptor, the relative concentrations of the agonist [D] and antagonist [A].

What does the Gaddum equation describe?

relates the occupancy of receptors by the agonist and the concentrations of the agonist and antagonist.

What is the dose ratio (DR)?

the ratio of agonist concentrations that elicit the same response in the absence (D0) or presence (DA) of the antagonist

What does a dose ratio of 2 indicate?

antagonist concentration doubles the agonist's EC50, which equals its dissociation constant (Ka).

What is pA2 in pharmacology?

negative log of the antagonist concentration that produces a dose ratio of 2.

What happens if the response in the presence and absence of the antagonist is the same?

it can be assumed that the occupancy by the agonist is also the same.

how is DR calculated

DR = [DA]/[D0].