Pain: opioid conversion: practice question

A Anaesthesia 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.

Try it

Anaesthesia · Pain: opioid conversion

Sample item

A patient is taking 120 mg of oral morphine in 24 hours and becomes nil by mouth. Using an oral to intravenous ratio of 3 to 1, what is the approximate intravenous morphine requirement over 24 hours?

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

The answer and the reasoning

C. 40 mg

Oral morphine has roughly one third of the bioavailability of the parenteral route because of first-pass metabolism, so the intravenous dose is about one third of the oral dose. 120 mg divided by 3 gives 40 mg per 24 hours. Doses are then titrated to effect, and incomplete cross-tolerance usually justifies a cautious reduction when rotating between different opioids.

Option by option

  • A. 120 mg

    This assumes equal potency by both routes and would overdose the patient.

  • B. 360 mg

    This multiplies by 3 instead of dividing.

  • C. 40 mg (correct)

    Correct. 120 divided by 3 gives 40 mg.

  • D. 12 mg

    This divides by 10, which is not the standard ratio.

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.

More Anaesthesia questions

Questions about this Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is C, 40 mg. Oral morphine has roughly one third of the bioavailability of the parenteral route because of first-pass metabolism, so the intravenous dose is about one third of the oral dose.

Why is "120 mg" not the answer?

This assumes equal potency by both routes and would overdose the patient.

Why is "360 mg" not the answer?

This multiplies by 3 instead of dividing.

Why is "12 mg" not the answer?

This divides by 10, which is not the standard ratio.

What concept does this question test?

It tests Pain: opioid conversion in Anaesthesia. 120 mg divided by 3 gives 40 mg per 24 hours. Doses are then titrated to effect, and incomplete cross-tolerance usually justifies a cautious reduction when rotating between different opioids.

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 Pain: opioid conversion?

Make a table of each agent, its key advantage and its main side effect. Then use the flashcards and the other Anaesthesia 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.