Pharmacodynamics: tachyphylaxis: 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: tachyphylaxis

Sample item

A patient is given repeated doses of ephedrine every 15 minutes to correct hypotension. The pressor response becomes progressively smaller with each dose. What best explains this?

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

The answer and the reasoning

C. Depletion of noradrenaline stores in nerve terminals

Ephedrine acts partly indirectly by displacing noradrenaline from storage vesicles. With rapid repeated dosing the releasable stores are depleted, so the response falls quickly. This acute loss of response is tachyphylaxis, and it differs from tolerance that develops over days.

Option by option

  • A. Upregulation of beta receptors

    Receptor upregulation would increase, not decrease, responsiveness.

  • B. Increased renal excretion of ephedrine

    Excretion changes would not produce a fall within minutes between doses.

  • C. Depletion of noradrenaline stores in nerve terminals (correct)

    Correct. Rapid depletion of releasable transmitter reduces each successive response.

  • D. Hepatic enzyme induction

    Enzyme induction needs days and affects hepatically cleared drugs, not a response within an hour.

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.

More Pharmacology questions

Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is C, Depletion of noradrenaline stores in nerve terminals. Ephedrine acts partly indirectly by displacing noradrenaline from storage vesicles.

Why is "Upregulation of beta receptors" not the answer?

Receptor upregulation would increase, not decrease, responsiveness.

Why is "Increased renal excretion of ephedrine" not the answer?

Excretion changes would not produce a fall within minutes between doses.

Why is "Hepatic enzyme induction" not the answer?

Enzyme induction needs days and affects hepatically cleared drugs, not a response within an hour.

What concept does this question test?

It tests Pharmacodynamics: tachyphylaxis in Pharmacology. With rapid repeated dosing the releasable stores are depleted, so the response falls quickly. This acute loss of response is tachyphylaxis, and it differs from tolerance that develops over days.

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: tachyphylaxis?

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.