Drug interactions: CYP3A4 and food: 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 · Drug interactions: CYP3A4 and food

Sample item

A hypertensive patient on stable felodipine begins drinking a large glass of grapefruit juice every morning and develops flushing, ankle oedema and a low blood pressure. What is the mechanism?

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

The answer and the reasoning

A. Inhibition of intestinal CYP3A4, raising oral bioavailability

Furanocoumarins in grapefruit juice irreversibly inhibit CYP3A4 in the gut wall, reducing first-pass metabolism. Bioavailability of drugs such as felodipine rises and produces exaggerated vasodilatation. The effect lasts for a day or more because new enzyme must be synthesised.

Option by option

  • A. Inhibition of intestinal CYP3A4, raising oral bioavailability (correct)

    Correct. Reduced gut-wall metabolism increases systemic exposure to felodipine.

  • B. Induction of hepatic CYP2D6, increasing drug activation

    Felodipine is inactivated, not activated, by CYP3A4, and grapefruit inhibits rather than induces.

  • C. Displacement of felodipine from plasma albumin

    Albumin displacement is not the cause, and would only transiently raise free drug.

  • D. Reduced tubular secretion of felodipine in the kidney

    Felodipine is eliminated by hepatic metabolism, not by tubular secretion.

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 A, Inhibition of intestinal CYP3A4, raising oral bioavailability. Furanocoumarins in grapefruit juice irreversibly inhibit CYP3A4 in the gut wall, reducing first-pass metabolism.

Why is "Induction of hepatic CYP2D6, increasing drug activation" not the answer?

Felodipine is inactivated, not activated, by CYP3A4, and grapefruit inhibits rather than induces.

Why is "Displacement of felodipine from plasma albumin" not the answer?

Albumin displacement is not the cause, and would only transiently raise free drug.

Why is "Reduced tubular secretion of felodipine in the kidney" not the answer?

Felodipine is eliminated by hepatic metabolism, not by tubular secretion.

What concept does this question test?

It tests Drug interactions: CYP3A4 and food in Pharmacology. Bioavailability of drugs such as felodipine rises and produces exaggerated vasodilatation. The effect lasts for a day or more because new enzyme must be synthesised.

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 Drug interactions: CYP3A4 and food?

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.