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

Step 1: What is competitive antagonism?
Competitive antagonism occurs when an antagonist competes with the agonist for the same binding site on the receptor. This is also called surmountable antagonism because the effect can be overcome.

Step 2: Key features of competitive antagonism.
Both agonist and antagonist bind to the same (orthosteric) receptor site. The antagonism is reversible. Increasing agonist concentration can displace the antagonist and restore the full effect. On a log dose-response curve, the agonist curve shifts to the RIGHT (not left) in the presence of the antagonist, with the same maximum effect.

Step 3: Evaluate each option.
Option 1 is false: competitive antagonism CAN be reversed by increasing agonist dose. Option 2 is false: the agonist CAN displace the antagonist from the receptor by mass action. Option 3 is TRUE: agonists and antagonists bind to the same receptor in competitive antagonism. Option 4 is false: the dose-response curve shifts to the RIGHT (not left) in competitive antagonism.

Step 4: Why Option 3 is uniquely true.
The hallmark of competitive antagonism is that the antagonist and agonist compete for the same binding site. This is what makes it 'competitive.'

Step 5: Conclusion.
The correct statement about competitive antagonism is that both agonists and antagonists bind to the same receptor.


Answer: Option (3) — Agonists and antagonists bind to the same receptor