Local anaesthetics: prilocaine methaemoglobinaemia: 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 · Local anaesthetics: prilocaine methaemoglobinaemia

Sample item

A neonate given a large dose of prilocaine cream becomes cyanosed with a low saturation on pulse oximetry that does not improve with oxygen, and blood appears chocolate brown. What is the antidote?

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

The answer and the reasoning

C. Methylene blue

A metabolite of prilocaine, o-toluidine, oxidises haemoglobin iron to the ferric state, producing methaemoglobinaemia. Methylene blue reduces methaemoglobin to haemoglobin, and it is avoided in G6PD deficiency.

Option by option

  • A. Naloxone

    Naloxone has no role.

  • B. Hydroxocobalamin

    Hydroxocobalamin treats cyanide poisoning.

  • C. Methylene blue (correct)

    Correct. Methylene blue reduces methaemoglobin.

  • D. Sodium nitrite

    Sodium nitrite itself induces methaemoglobin.

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 C, Methylene blue. A metabolite of prilocaine, o-toluidine, oxidises haemoglobin iron to the ferric state, producing methaemoglobinaemia.

Why is "Naloxone" not the answer?

Naloxone has no role.

Why is "Hydroxocobalamin" not the answer?

Hydroxocobalamin treats cyanide poisoning.

Why is "Sodium nitrite" not the answer?

Sodium nitrite itself induces methaemoglobin.

What concept does this question test?

It tests Local anaesthetics: prilocaine methaemoglobinaemia in Pharmacology. Methylene blue reduces methaemoglobin to haemoglobin, and it is avoided in G6PD deficiency.

How hard is this question?

We tag it as a multi-step question: it asks you to combine more than one idea. 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 Local anaesthetics: prilocaine methaemoglobinaemia?

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.