Sedative-hypnotics: mechanism: 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 · Sedative-hypnotics: mechanism

Sample item

Which statement correctly distinguishes how benzodiazepines and barbiturates act at the GABA-A receptor?

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

The answer and the reasoning

B. Benzodiazepines increase the frequency of channel opening, whereas barbiturates prolong the duration and can open the channel directly at high doses

Benzodiazepines bind the interface between alpha and gamma subunits and increase how often GABA opens the chloride channel, which needs GABA to be present. Barbiturates bind elsewhere, prolong the opening time and at high doses open the channel without GABA. This explains the ceiling effect of benzodiazepines and the dangerous respiratory depression of barbiturate overdose.

Option by option

  • A. Both open the chloride channel directly in the absence of GABA at therapeutic doses

    Benzodiazepines need GABA, so they cannot open the channel by themselves.

  • B. Benzodiazepines increase the frequency of channel opening, whereas barbiturates prolong the duration and can open the channel directly at high doses (correct)

    Frequency versus duration, with direct gating by barbiturates at high dose, is correct.

  • C. Benzodiazepines prolong channel opening and barbiturates increase its frequency, and neither acts without GABA

    The two patterns are reversed here, and barbiturates can act without GABA at high dose.

  • D. Benzodiazepines block the channel and barbiturates enhance glycine receptors

    Benzodiazepines potentiate GABA and do not block the channel or act on glycine receptors.

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.

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Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is B, Benzodiazepines increase the frequency of channel opening, whereas barbiturates prolong the duration and can open the channel directly at high doses. Benzodiazepines bind the interface between alpha and gamma subunits and increase how often GABA opens the chloride channel, which needs GABA to be present.

Why is "Both open the chloride channel directly in the absence of GABA at the…" not the answer?

Benzodiazepines need GABA, so they cannot open the channel by themselves.

Why is "Benzodiazepines prolong channel opening and barbiturates increase its…" not the answer?

The two patterns are reversed here, and barbiturates can act without GABA at high dose.

Why is "Benzodiazepines block the channel and barbiturates enhance glycine re…" not the answer?

Benzodiazepines potentiate GABA and do not block the channel or act on glycine receptors.

What concept does this question test?

It tests Sedative-hypnotics: mechanism in Pharmacology. Barbiturates bind elsewhere, prolong the opening time and at high doses open the channel without GABA. This explains the ceiling effect of benzodiazepines and the dangerous respiratory depression of barbiturate overdose.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Sedative-hypnotics: mechanism?

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.