General pharmacology and pharmacokinetics: active metabolites: 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 and pharmacokinetics: active metabolites

Sample item

An elderly man is drowsy and unsteady for three days after taking one dose of diazepam at night for insomnia. Which feature of diazepam best explains the prolonged effect?

ADelayed absorption from the gutBFormation of a long-lived active metaboliteCSaturable zero-order elimination at this doseDAutoinduction of its own metabolism

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

The answer and the reasoning

B. Formation of a long-lived active metabolite

Diazepam is converted to desmethyldiazepam, an active metabolite with a half-life of many hours that is cleared even more slowly in the elderly. This explains the hangover and the cumulative effect on repeated dosing.

Option by option

A. Delayed absorption from the gut
Diazepam is absorbed rapidly after an oral dose, so slow absorption does not explain days of drowsiness.
B. Formation of a long-lived active metabolite (correct)
Correct. The active metabolite persists for days in the elderly and keeps producing sedation.
C. Saturable zero-order elimination at this dose
Zero-order kinetics occurs with drugs such as phenytoin and alcohol, not with diazepam at hypnotic doses.
D. Autoinduction of its own metabolism
Autoinduction would shorten the effect, whereas this patient shows prolongation.

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, Formation of a long-lived active metabolite. Diazepam is converted to desmethyldiazepam, an active metabolite with a half-life of many hours that is cleared even more slowly in the elderly.

Why is "Delayed absorption from the gut" not the answer?

Diazepam is absorbed rapidly after an oral dose, so slow absorption does not explain days of drowsiness.

Why is "Saturable zero-order elimination at this dose" not the answer?

Zero-order kinetics occurs with drugs such as phenytoin and alcohol, not with diazepam at hypnotic doses.

Why is "Autoinduction of its own metabolism" not the answer?

Autoinduction would shorten the effect, whereas this patient shows prolongation.

What concept does this question test?

It tests General pharmacology and pharmacokinetics: active metabolites in Pharmacology. This explains the hangover and the cumulative effect on repeated dosing.

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 and pharmacokinetics: active metabolites?

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.