General pharmacology: time to 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 · General pharmacology: time to steady state

Sample item

A patient is on a constant intravenous infusion of a drug with a half-life of 6 hours. The infusion rate is doubled. Roughly how long will it take to reach the new steady state?

AAbout 48 to 60 hours, because the plateau is higherBAbout 6 hours, one half-lifeCAbout 12 hours, because the rate is doubledDAbout 24 to 30 hours, the same as before the change

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

The answer and the reasoning

D. About 24 to 30 hours, the same as before the change

Time to steady state depends only on the elimination half-life, about 4 to 5 half-lives, and not on the dose or infusion rate. A higher rate changes the height of the plateau but not the time taken to reach it.

Option by option

A. About 48 to 60 hours, because the plateau is higher
A higher plateau does not lengthen the time needed, since time depends on half-life alone.
B. About 6 hours, one half-life
One half-life reaches only 50 percent of the new steady state.
C. About 12 hours, because the rate is doubled
Doubling the rate doubles the plateau concentration, not the speed of approach to it.
D. About 24 to 30 hours, the same as before the change (correct)
Correct. Five half-lives of 6 hours is about 30 hours regardless of the infusion rate.

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, About 24 to 30 hours, the same as before the change. Time to steady state depends only on the elimination half-life, about 4 to 5 half-lives, and not on the dose or infusion rate.

Why is "About 48 to 60 hours, because the plateau is higher" not the answer?

A higher plateau does not lengthen the time needed, since time depends on half-life alone.

Why is "About 6 hours, one half-life" not the answer?

One half-life reaches only 50 percent of the new steady state.

Why is "About 12 hours, because the rate is doubled" not the answer?

Doubling the rate doubles the plateau concentration, not the speed of approach to it.

What concept does this question test?

It tests General pharmacology: time to steady state in Pharmacology. A higher rate changes the height of the plateau but not the time taken to reach it.

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 General pharmacology: time to 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.