Pharmacokinetics: bioavailability from AUC: 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: bioavailability from AUC

Sample item

A drug is given as 200 mg orally and the area under the plasma concentration-time curve is 30 mg.h/L. When 100 mg of the same drug is given intravenously, the area under the curve is 25 mg.h/L. What is the oral bioavailability?

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

The answer and the reasoning

C. 60 percent

Absolute bioavailability is the dose-corrected AUC after oral dosing divided by the dose-corrected AUC after intravenous dosing. Oral: 30 / 200 = 0.15; intravenous: 25 / 100 = 0.25. F = 0.15 / 0.25 = 0.6, or 60 percent.

Option by option

  • A. 40 percent

    This does not follow from the dose-corrected AUC ratio; it would need the oral AUC to be much lower than observed.

  • B. 83 percent

    This is 25/30, the inverted ratio of the raw AUCs, and ignores that the oral dose was double the intravenous dose.

  • C. 60 percent (correct)

    Correct. F = (30/200) / (25/100) = 0.6.

  • D. 120 percent

    This is the raw AUC ratio 30/25 with no dose correction; bioavailability cannot exceed 100 percent.

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, 60 percent. Absolute bioavailability is the dose-corrected AUC after oral dosing divided by the dose-corrected AUC after intravenous dosing.

Why is "40 percent" not the answer?

This does not follow from the dose-corrected AUC ratio; it would need the oral AUC to be much lower than observed.

Why is "83 percent" not the answer?

This is 25/30, the inverted ratio of the raw AUCs, and ignores that the oral dose was double the intravenous dose.

Why is "120 percent" not the answer?

This is the raw AUC ratio 30/25 with no dose correction; bioavailability cannot exceed 100 percent.

What concept does this question test?

It tests Pharmacokinetics: bioavailability from AUC in Pharmacology. Oral: 30 / 200 = 0.15; intravenous: 25 / 100 = 0.25. F = 0.15 / 0.25 = 0.6, or 60 percent.

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: bioavailability from AUC?

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.