Pharmacokinetics: maintenance dose calculation: 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: maintenance dose calculation

Sample item

An oral drug has a clearance of 3 L per hour and a bioavailability of 50 percent. It is to be given every 12 hours to achieve an average steady-state plasma concentration of 10 mg/L. What dose should be given at each interval?

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

The answer and the reasoning

C. 720 mg

Dosing rate = target concentration x clearance / bioavailability = 10 x 3 / 0.5 = 60 mg per hour. Over a 12-hour interval the dose is 60 x 12 = 720 mg. Bioavailability divides the dose because only half of each oral dose reaches the circulation.

Option by option

  • A. 1440 mg

    This corresponds to a 24-hour interval, not the 12-hour interval specified.

  • B. 360 mg

    This ignores bioavailability and would give only half the intended average concentration.

  • C. 720 mg (correct)

    Correct. (10 x 3 x 12) / 0.5 = 720 mg.

  • D. 180 mg

    This multiplies by bioavailability instead of dividing by it.

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 C, 720 mg. Dosing rate = target concentration x clearance / bioavailability = 10 x 3 / 0.

Why is "1440 mg" not the answer?

This corresponds to a 24-hour interval, not the 12-hour interval specified.

Why is "360 mg" not the answer?

This ignores bioavailability and would give only half the intended average concentration.

Why is "180 mg" not the answer?

This multiplies by bioavailability instead of dividing by it.

What concept does this question test?

It tests Pharmacokinetics: maintenance dose calculation in Pharmacology. 5 = 60 mg per hour. Over a 12-hour interval the dose is 60 x 12 = 720 mg. Bioavailability divides the dose because only half of each oral dose reaches the circulation.

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 Pharmacokinetics: maintenance dose calculation?

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.