General pharmacology: non-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 · General pharmacology: non-competitive antagonism

Sample item

Phenoxybenzamine binds covalently to alpha adrenoceptors. What happens to the noradrenaline dose-response curve after adequate dosing?

AThe maximal response is depressed and cannot be restored by higher noradrenaline dosesBThe curve shifts right in parallel and the maximum is preservedCThe curve shifts leftDPotency increases while efficacy is unchanged

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

The answer and the reasoning

A. The maximal response is depressed and cannot be restored by higher noradrenaline doses

Irreversible binding removes functional receptors, so even very high agonist concentrations cannot produce the original maximal effect. This is non-competitive (insurmountable) antagonism.

Option by option

A. The maximal response is depressed and cannot be restored by higher noradrenaline doses (correct)
Correct. Receptor loss lowers the maximum, which cannot be overcome.
B. The curve shifts right in parallel and the maximum is preserved
A parallel shift with preserved maximum is competitive antagonism.
C. The curve shifts left
A left shift would suggest increased sensitivity, not antagonism.
D. Potency increases while efficacy is unchanged
Antagonism reduces effect and does not raise potency.

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 A, The maximal response is depressed and cannot be restored by higher noradrenaline doses. Irreversible binding removes functional receptors, so even very high agonist concentrations cannot produce the original maximal effect.

Why is "The curve shifts right in parallel and the maximum is preserved" not the answer?

A parallel shift with preserved maximum is competitive antagonism.

Why is "The curve shifts left" not the answer?

A left shift would suggest increased sensitivity, not antagonism.

Why is "Potency increases while efficacy is unchanged" not the answer?

Antagonism reduces effect and does not raise potency.

What concept does this question test?

It tests General pharmacology: non-competitive antagonism in Pharmacology. This is non-competitive (insurmountable) antagonism.

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 General pharmacology: non-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.