Question

Which one of the following is true about a competitive antagonism?

• A. Antagonism cannot be completely reversed by increased dose of the agonist
• B. An agonist cannot displace an antagonist from the receptor
• C. Agonists and antagonists bind to the same receptor
• D. Dose-response curve of an agonists shifts to the left in the presence of an antagonist

Hint:

A competitive antagonist is a drug that binds to the same receptor site as the agonist but produces no effect itself. It simply "competes" with the agonist for that binding site.

Answer 1

The Correct Option is C

Concept:
A competitive antagonist is a drug that binds to the same receptor site as the agonist but produces no effect itself. It simply "competes" with the agonist for that binding site. Understanding this competition explains all the key features of competitive antagonism.

Step 1: Because both the agonist and the competitive antagonist bind to the same receptor, they are fighting over the same site. This is the defining feature of competitive antagonism.

Step 2: Since the binding is reversible and at the same site, adding more agonist can out-compete the antagonist and fully restore the maximum response. This shifts the agonist dose-response curve to the RIGHT (not left), without reducing the maximum effect. So the statements about non-reversibility, inability to displace, and a left shift are all incorrect.

Answer: Option (3) — In competitive antagonism, agonists and antagonists bind to the same receptor. (3)