Pharmacodynamics: competitive antagonism: practice question

A Pharmacology question in the style of the NEET PG paper. Answer it first, then read why the right option is right and why each of the others is wrong.

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Pharmacology · Pharmacodynamics: competitive antagonism

Sample item

A reversible competitive antagonist is added to a tissue preparation and the agonist dose-response curve is repeated. What change is expected?

ANo shift but a flattened curve with a lower slopeBParallel rightward shift with the same maximal responseCRightward shift with a reduced maximal responseDLeftward shift with the same maximal response

Original practice item, not a recalled exam question. Nothing here is recorded.

The answer and the reasoning

B. Parallel rightward shift with the same maximal response

A reversible competitive antagonist occupies the same site as the agonist, so more agonist is needed to achieve a given effect. The curve shifts to the right in parallel (higher EC50), and the maximal response is unchanged because a high agonist concentration can overcome the block. An irreversible or non-competitive antagonist lowers the maximum.

Option by option

A. No shift but a flattened curve with a lower slope
A reversible competitive antagonist changes position of the curve rather than flattening it.
B. Parallel rightward shift with the same maximal response (correct)
Correct. Surmountable antagonism raises the EC50 but not the Emax.
C. Rightward shift with a reduced maximal response
A reduced maximum is the signature of irreversible or non-competitive antagonism.
D. Leftward shift with the same maximal response
A leftward shift would indicate increased potency, as with a positive modulator.

Source note: Original NextPrep sample item — pending expert review. This item is original practice material awaiting independent expert review, so confirm important facts in a standard textbook.

Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is B, Parallel rightward shift with the same maximal response. A reversible competitive antagonist occupies the same site as the agonist, so more agonist is needed to achieve a given effect.

Why is "No shift but a flattened curve with a lower slope" not the answer?

A reversible competitive antagonist changes position of the curve rather than flattening it.

Why is "Rightward shift with a reduced maximal response" not the answer?

A reduced maximum is the signature of irreversible or non-competitive antagonism.

Why is "Leftward shift with the same maximal response" not the answer?

A leftward shift would indicate increased potency, as with a positive modulator.

What concept does this question test?

It tests Pharmacodynamics: competitive antagonism in Pharmacology. The curve shifts to the right in parallel (higher EC50), and the maximal response is unchanged because a high agonist concentration can overcome the block. An irreversible or non-competitive antagonist lowers the maximum.

How hard is this question?

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

How should I study Pharmacodynamics: competitive antagonism?

Learn drugs as classes, then the exception in each class that an examiner would pick. Then use the flashcards and the other Pharmacology questions on this site to test what stuck.

Is this a real NEET PG question?

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.