Pharmacokinetics: 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

Sample item

A drug has an apparent volume of distribution of several hundred litres in an adult. What does this most likely indicate?

AVery rapid renal eliminationBConfinement of the drug mainly to plasma, bound to albuminCRestriction of the drug to extracellular fluid because it is highly ionisedDExtensive distribution into and binding in tissues, leaving little in plasma

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

The answer and the reasoning

D. Extensive distribution into and binding in tissues, leaving little in plasma

Volume of distribution is the dose divided by plasma concentration and is only an apparent volume. A value far larger than total body water means the drug is concentrated in tissues such as fat or bound to tissue components, so the plasma level is low.

Option by option

A. Very rapid renal elimination
Volume of distribution describes distribution, not elimination speed, which is described by clearance.
B. Confinement of the drug mainly to plasma, bound to albumin
Drugs confined to plasma have a small volume, around 3 to 5 litres.
C. Restriction of the drug to extracellular fluid because it is highly ionised
Drugs restricted to extracellular fluid have a modest volume of around 12 to 20 litres, not hundreds.
D. Extensive distribution into and binding in tissues, leaving little in plasma (correct)
Correct. Tissue sequestration lowers the plasma concentration, producing a very large apparent volume.

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 D, Extensive distribution into and binding in tissues, leaving little in plasma. Volume of distribution is the dose divided by plasma concentration and is only an apparent volume.

Why is "Very rapid renal elimination" not the answer?

Volume of distribution describes distribution, not elimination speed, which is described by clearance.

Why is "Confinement of the drug mainly to plasma, bound to albumin" not the answer?

Drugs confined to plasma have a small volume, around 3 to 5 litres.

Why is "Restriction of the drug to extracellular fluid because it is highly i…" not the answer?

Drugs restricted to extracellular fluid have a modest volume of around 12 to 20 litres, not hundreds.

What concept does this question test?

It tests Pharmacokinetics in Pharmacology. A value far larger than total body water means the drug is concentrated in tissues such as fat or bound to tissue components, so the plasma level is low.

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?

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.