Oral and maxillofacial surgery and facial fractures: prilocaine methaemoglobinaemia: practice question

A Dentistry 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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Dentistry · Oral and maxillofacial surgery and facial fractures: prilocaine methaemoglobinaemia

Sample item

After a large dose of dental local anaesthetic, a patient develops cyanosis with chocolate-brown blood but a normal arterial oxygen tension and no respiratory distress. Which drug is the most likely cause, and what is the treatment?

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

The answer and the reasoning

A. Prilocaine, treated with intravenous methylene blue

Prilocaine is metabolised to o-toluidine, which oxidises haemoglobin to methaemoglobin and causes cyanosis despite normal PaO2. Symptomatic methaemoglobinaemia is treated with oxygen and intravenous methylene blue. The risk rises with large doses.

Option by option

  • A. Prilocaine, treated with intravenous methylene blue (correct)

    Correct. Prilocaine causes methaemoglobinaemia that responds to methylene blue.

  • B. Bupivacaine, treated with atropine

    Atropine treats bradycardia and not methaemoglobin, and bupivacaine is not the usual cause.

  • C. Lignocaine, treated with naloxone

    Lignocaine does not usually cause this, and naloxone is an opioid antagonist.

  • D. Mepivacaine, treated with flumazenil

    Flumazenil reverses benzodiazepines and has no role here.

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 Dentistry question

What is the answer to this Dentistry question?

The best answer is A, Prilocaine, treated with intravenous methylene blue. Prilocaine is metabolised to o-toluidine, which oxidises haemoglobin to methaemoglobin and causes cyanosis despite normal PaO2.

Why is "Bupivacaine, treated with atropine" not the answer?

Atropine treats bradycardia and not methaemoglobin, and bupivacaine is not the usual cause.

Why is "Lignocaine, treated with naloxone" not the answer?

Lignocaine does not usually cause this, and naloxone is an opioid antagonist.

Why is "Mepivacaine, treated with flumazenil" not the answer?

Flumazenil reverses benzodiazepines and has no role here.

What concept does this question test?

It tests Oral and maxillofacial surgery and facial fractures: prilocaine methaemoglobinaemia in Dentistry. Symptomatic methaemoglobinaemia is treated with oxygen and intravenous methylene blue. The risk rises with large doses.

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 Oral and maxillofacial surgery and facial fractures: prilocaine methaemoglobinaemia?

Learn the dental formula, eruption ages and tooth structure once, as tables. Then use the flashcards and the other Dentistry 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.