Pharmacokinetics: maintenance dose: 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

Sample item

A drug has a clearance of 2 L/h and an oral bioavailability of 0.8. A steady-state plasma concentration of 5 mg/L is required. What oral dose given every 12 hours is needed?

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

The answer and the reasoning

A. 150 mg

At steady state the dosing rate equals clearance times target concentration divided by bioavailability. Here 2 L/h x 5 mg/L = 10 mg/h absorbed, and 10 / 0.8 = 12.5 mg/h must be given. Over 12 hours this is 12.5 x 12 = 150 mg.

Option by option

  • A. 150 mg (correct)

    Correct. 12.5 mg/h x 12 h = 150 mg every 12 hours after correcting for bioavailability.

  • B. 96 mg

    This multiplies by 0.8 instead of dividing, which lowers the dose instead of raising it.

  • C. 120 mg

    This is 10 mg/h x 12 h and ignores bioavailability, so it would under-dose.

  • D. 300 mg

    This is 12.5 mg/h x 24 h, the daily total, not the dose for a 12-hour interval.

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, 150 mg. At steady state the dosing rate equals clearance times target concentration divided by bioavailability.

Why is "96 mg" not the answer?

This multiplies by 0.8 instead of dividing, which lowers the dose instead of raising it.

Why is "120 mg" not the answer?

This is 10 mg/h x 12 h and ignores bioavailability, so it would under-dose.

Why is "300 mg" not the answer?

This is 12.5 mg/h x 24 h, the daily total, not the dose for a 12-hour interval.

What concept does this question test?

It tests Pharmacokinetics: maintenance dose in Pharmacology. Here 2 L/h x 5 mg/L = 10 mg/h absorbed, and 10 / 0.8 = 12.5 mg/h must be given. Over 12 hours this is 12.5 x 12 = 150 mg.

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?

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.