General pharmacology and pharmacokinetics: carrier-mediated absorption: 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 and pharmacokinetics: carrier-mediated absorption

Sample item

A man with Parkinson disease on levodopa notices more off periods after he switches to a diet very high in protein. Which mechanism best explains this change?

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

The answer and the reasoning

B. Competition for the amino acid carrier

Levodopa is absorbed from the small intestine and enters the brain through the large neutral amino acid carrier. Dietary amino acids compete for the same carrier, lowering absorption and central entry. Spacing doses away from protein meals helps.

Option by option

  • A. Increased renal tubular secretion of levodopa

    Renal secretion is not altered by dietary protein in a way that explains the change.

  • B. Competition for the amino acid carrier (correct)

    Correct. Amino acids compete with levodopa for the shared carrier in gut and at the blood-brain barrier.

  • C. Chelation of levodopa by dietary protein

    Protein does not chelate levodopa; chelation is a feature of iron and tetracycline.

  • D. Induction of dopa decarboxylase in the gut

    Decarboxylase is inhibited by carbidopa and is not induced by dietary protein.

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 B, Competition for the amino acid carrier. Levodopa is absorbed from the small intestine and enters the brain through the large neutral amino acid carrier.

Why is "Increased renal tubular secretion of levodopa" not the answer?

Renal secretion is not altered by dietary protein in a way that explains the change.

Why is "Chelation of levodopa by dietary protein" not the answer?

Protein does not chelate levodopa; chelation is a feature of iron and tetracycline.

Why is "Induction of dopa decarboxylase in the gut" not the answer?

Decarboxylase is inhibited by carbidopa and is not induced by dietary protein.

What concept does this question test?

It tests General pharmacology and pharmacokinetics: carrier-mediated absorption in Pharmacology. Dietary amino acids compete for the same carrier, lowering absorption and central entry. Spacing doses away from protein meals helps.

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 General pharmacology and pharmacokinetics: carrier-mediated absorption?

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.