Papulosquamous disorders: methotrexate toxicity: practice question

A Dermatology 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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Dermatology · Papulosquamous disorders: methotrexate toxicity

Sample item

A psoriasis patient on weekly methotrexate develops mouth ulcers and pancytopenia after accidentally taking the dose daily. Which is the specific rescue agent?

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

The answer and the reasoning

B. Folinic acid (leucovorin)

Methotrexate inhibits dihydrofolate reductase, and leucovorin bypasses the block by supplying reduced folate. Folic acid supplementation is used to prevent toxicity, but overdose needs folinic acid.

Option by option

  • A. Folic acid alone

    Folic acid alone requires reduction by DHFR, which is blocked.

  • B. Folinic acid (leucovorin) (correct)

    Correct. Leucovorin rescues cells in methotrexate toxicity.

  • C. Pyridoxine

    Pyridoxine is used for isoniazid toxicity.

  • D. Vitamin B12

    Vitamin B12 does not reverse DHFR inhibition.

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 Dermatology question

What is the answer to this Dermatology question?

The best answer is B, Folinic acid (leucovorin). Methotrexate inhibits dihydrofolate reductase, and leucovorin bypasses the block by supplying reduced folate.

Why is "Folic acid alone" not the answer?

Folic acid alone requires reduction by DHFR, which is blocked.

Why is "Pyridoxine" not the answer?

Pyridoxine is used for isoniazid toxicity.

Why is "Vitamin B12" not the answer?

Vitamin B12 does not reverse DHFR inhibition.

What concept does this question test?

It tests Papulosquamous disorders: methotrexate toxicity in Dermatology. Folic acid supplementation is used to prevent toxicity, but overdose needs folinic acid.

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 Papulosquamous disorders: methotrexate toxicity?

Learn each condition by its primary lesion, site and signature sign. Then use the flashcards and the other Dermatology 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.