Chemotherapy: isoniazid neuropathy: 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 · Chemotherapy: isoniazid neuropathy

Sample item

A 50-year-old diabetic man on antitubercular therapy has numbness and tingling in both feet. Which agent should be added and why?

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

The answer and the reasoning

D. Pyridoxine, because isoniazid depletes pyridoxal phosphate

Isoniazid forms a hydrazone with pyridoxal and increases urinary excretion of pyridoxine, so peripheral neuropathy develops, especially in slow acetylators, diabetics, alcoholics and the malnourished. Pyridoxine 10 mg per day prevents it in at-risk patients. Higher doses are used for treatment, and the antitubercular drug is not stopped.

Option by option

  • A. Vitamin B12, because isoniazid blocks its absorption

    Isoniazid is not known to block B12 absorption.

  • B. Folic acid, because isoniazid inhibits dihydrofolate reductase

    Isoniazid does not inhibit dihydrofolate reductase; methotrexate and trimethoprim do.

  • C. Vitamin K, because isoniazid inhibits clotting factor synthesis

    Vitamin K deficiency is not a feature of isoniazid therapy.

  • D. Pyridoxine, because isoniazid depletes pyridoxal phosphate (correct)

    Correct. Replacing pyridoxine corrects the functional deficiency.

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 D, Pyridoxine, because isoniazid depletes pyridoxal phosphate. Isoniazid forms a hydrazone with pyridoxal and increases urinary excretion of pyridoxine, so peripheral neuropathy develops, especially in slow acetylators, diabetics, alcoholics and the malnourished.

Why is "Vitamin B12, because isoniazid blocks its absorption" not the answer?

Isoniazid is not known to block B12 absorption.

Why is "Folic acid, because isoniazid inhibits dihydrofolate reductase" not the answer?

Isoniazid does not inhibit dihydrofolate reductase; methotrexate and trimethoprim do.

Why is "Vitamin K, because isoniazid inhibits clotting factor synthesis" not the answer?

Vitamin K deficiency is not a feature of isoniazid therapy.

What concept does this question test?

It tests Chemotherapy: isoniazid neuropathy in Pharmacology. Pyridoxine 10 mg per day prevents it in at-risk patients. Higher doses are used for treatment, and the antitubercular drug is not stopped.

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 Chemotherapy: isoniazid neuropathy?

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.