Nucleotide drugs: mycophenolate: practice question

A Biochemistry 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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Biochemistry · Nucleotide drugs: mycophenolate

Sample item

A renal transplant recipient is given mycophenolate mofetil. Which mechanism explains its immunosuppressive effect?

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

The answer and the reasoning

D. Inhibition of IMP dehydrogenase, depleting guanine nucleotides in proliferating lymphocytes

Mycophenolic acid is a reversible inhibitor of IMP dehydrogenase, the rate-limiting enzyme for GMP synthesis. T and B lymphocytes rely heavily on de novo purine synthesis, so they are depleted of guanine nucleotides while other cells can use salvage. Common adverse effects are diarrhoea and leucopenia.

Option by option

  • A. Inhibition of mTOR kinase

    mTOR inhibition is the action of sirolimus and everolimus.

  • B. Inhibition of dihydrofolate reductase

    Dihydrofolate reductase inhibition is the action of methotrexate.

  • C. Inhibition of calcineurin

    Calcineurin inhibition is the action of tacrolimus and ciclosporin.

  • D. Inhibition of IMP dehydrogenase, depleting guanine nucleotides in proliferating lymphocytes (correct)

    Correct. IMPDH blockade selectively limits lymphocyte proliferation.

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 Biochemistry question

What is the answer to this Biochemistry question?

The best answer is D, Inhibition of IMP dehydrogenase, depleting guanine nucleotides in proliferating lymphocytes. Mycophenolic acid is a reversible inhibitor of IMP dehydrogenase, the rate-limiting enzyme for GMP synthesis.

Why is "Inhibition of mTOR kinase" not the answer?

mTOR inhibition is the action of sirolimus and everolimus.

Why is "Inhibition of dihydrofolate reductase" not the answer?

Dihydrofolate reductase inhibition is the action of methotrexate.

Why is "Inhibition of calcineurin" not the answer?

Calcineurin inhibition is the action of tacrolimus and ciclosporin.

What concept does this question test?

It tests Nucleotide drugs: mycophenolate in Biochemistry. T and B lymphocytes rely heavily on de novo purine synthesis, so they are depleted of guanine nucleotides while other cells can use salvage. Common adverse effects are diarrhoea and leucopenia.

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 Nucleotide drugs: mycophenolate?

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry 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.