Pharmacokinetics: steady state: 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: steady state

Sample item

A drug with a half-life of 6 hours is given by constant intravenous infusion. About how long will it take to reach approximately 94% of the steady-state concentration?

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

The answer and the reasoning

C. 24 hours

Each half-life covers half of the remaining distance to steady state: 50% at one half-life, 75% at two, 87.5% at three and about 94% at four. Four half-lives is 24 hours; 4 to 5 half-lives is the usual rule for reaching steady state, regardless of the infusion rate.

Option by option

  • A. 6 hours

    After one half-life the concentration is only 50% of steady state.

  • B. 60 hours

    Ten half-lives would exceed what is needed; steady state is effectively reached in 4 to 5.

  • C. 24 hours (correct)

    Correct. Four half-lives (24 hours) gives about 94%.

  • D. 12 hours

    After two half-lives the concentration is about 75% of steady state.

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 C, 24 hours. Each half-life covers half of the remaining distance to steady state: 50% at one half-life, 75% at two, 87.

Why is "6 hours" not the answer?

After one half-life the concentration is only 50% of steady state.

Why is "60 hours" not the answer?

Ten half-lives would exceed what is needed; steady state is effectively reached in 4 to 5.

Why is "12 hours" not the answer?

After two half-lives the concentration is about 75% of steady state.

What concept does this question test?

It tests Pharmacokinetics: steady state in Pharmacology. 5% at three and about 94% at four. Four half-lives is 24 hours; 4 to 5 half-lives is the usual rule for reaching steady state, regardless of the infusion rate.

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: steady state?

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.