Pharmacokinetics: half-life: 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 · Pharmacokinetics: half-life

Sample item

A drug has an apparent volume of distribution of 70 L and a clearance of 7 L/h. What is its approximate elimination half-life?

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

The answer and the reasoning

A. About 7 hours

Half-life = 0.693 x Vd / CL. Here 0.693 x 70 / 7 = 0.693 x 10, which is about 6.9 hours. Half-life rises with a larger volume of distribution and falls with higher clearance.

Option by option

  • A. About 7 hours (correct)

    Correct. 0.693 x 70 / 7 is about 6.9 hours.

  • B. About 0.07 hour

    This inverts the ratio (0.693 x CL / Vd), which is not the half-life relationship.

  • C. About 49 hours

    This is 0.693 x 70 and ignores clearance altogether.

  • D. About 10 hours

    This is Vd / CL, the mean residence time of 10 hours, and omits the 0.693 factor.

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 A, About 7 hours. Half-life = 0.

Why is "About 0.07 hour" not the answer?

This inverts the ratio (0.693 x CL / Vd), which is not the half-life relationship.

Why is "About 49 hours" not the answer?

This is 0.693 x 70 and ignores clearance altogether.

Why is "About 10 hours" not the answer?

This is Vd / CL, the mean residence time of 10 hours, and omits the 0.693 factor.

What concept does this question test?

It tests Pharmacokinetics: half-life in Pharmacology. 693 x Vd / CL. Here 0.693 x 70 / 7 = 0.693 x 10, which is about 6.9 hours. Half-life rises with a larger volume of distribution and falls with higher clearance.

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 Pharmacokinetics: half-life?

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.