General pharmacology and pharmacokinetics: P-glycoprotein: 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: P-glycoprotein

Sample item

Loperamide is an opioid agonist that normally causes no central effects, yet volunteers given loperamide with quinidine developed respiratory depression. Which transporter did quinidine inhibit to produce this effect?

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

The answer and the reasoning

A. P-glycoprotein efflux pump

P-glycoprotein in brain capillary endothelium pumps loperamide back into blood and keeps it out of the brain. Quinidine inhibits this pump, so loperamide reaches mu receptors in the brainstem. P-glycoprotein also affects digoxin and many cancer drugs.

Option by option

  • A. P-glycoprotein efflux pump (correct)

    Correct. Inhibiting the efflux pump at the blood-brain barrier lets loperamide enter the brain.

  • B. Organic cation transporter OCT2

    OCT2 mediates renal secretion of cations such as metformin and does not protect the brain.

  • C. Organic anion transporter OAT1

    OAT1 handles renal secretion of organic anions and does not guard the brain from loperamide.

  • D. Uric acid transporter URAT1

    URAT1 reabsorbs urate in the proximal tubule and is unrelated to brain entry.

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, P-glycoprotein efflux pump. P-glycoprotein in brain capillary endothelium pumps loperamide back into blood and keeps it out of the brain.

Why is "Organic cation transporter OCT2" not the answer?

OCT2 mediates renal secretion of cations such as metformin and does not protect the brain.

Why is "Organic anion transporter OAT1" not the answer?

OAT1 handles renal secretion of organic anions and does not guard the brain from loperamide.

Why is "Uric acid transporter URAT1" not the answer?

URAT1 reabsorbs urate in the proximal tubule and is unrelated to brain entry.

What concept does this question test?

It tests General pharmacology and pharmacokinetics: P-glycoprotein in Pharmacology. Quinidine inhibits this pump, so loperamide reaches mu receptors in the brainstem. P-glycoprotein also affects digoxin and many cancer drugs.

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: P-glycoprotein?

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.