General pharmacology and pharmacokinetics: high extraction ratio drugs: 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.

Try it

Pharmacology · General pharmacology and pharmacokinetics: high extraction ratio drugs

Sample item

A drug has a hepatic extraction ratio of about 0.9. A patient with acute cardiac failure develops marked congestion and low output. Which change is most likely to lower the systemic clearance of this drug?

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

The answer and the reasoning

A. Reduced hepatic blood flow

For a drug that the liver removes almost completely in one pass, clearance approaches hepatic blood flow, so it is flow limited. Changes in enzyme activity or protein binding alter clearance very little. Propranolol, lidocaine and morphine behave this way.

Option by option

  • A. Reduced hepatic blood flow (correct)

    Correct. Clearance of a high extraction drug is limited by delivery to the liver, so lower flow lowers clearance.

  • B. Inhibition of its metabolising enzyme

    Inhibition has little effect on systemic clearance when extraction is already almost complete.

  • C. Reduced binding to plasma albumin

    Protein binding matters for low extraction drugs; here the liver strips drug off the carrier protein.

  • D. Induction of its metabolising enzyme

    Induction hardly changes clearance when the liver already removes nearly all drug presented to 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.

More Pharmacology questions

Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is A, Reduced hepatic blood flow. For a drug that the liver removes almost completely in one pass, clearance approaches hepatic blood flow, so it is flow limited.

Why is "Inhibition of its metabolising enzyme" not the answer?

Inhibition has little effect on systemic clearance when extraction is already almost complete.

Why is "Reduced binding to plasma albumin" not the answer?

Protein binding matters for low extraction drugs; here the liver strips drug off the carrier protein.

Why is "Induction of its metabolising enzyme" not the answer?

Induction hardly changes clearance when the liver already removes nearly all drug presented to it.

What concept does this question test?

It tests General pharmacology and pharmacokinetics: high extraction ratio drugs in Pharmacology. Changes in enzyme activity or protein binding alter clearance very little. Propranolol, lidocaine and morphine behave this way.

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 and pharmacokinetics: high extraction ratio drugs?

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.