Neuraxial opioids: fentanyl: 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.

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Anaesthesia · Neuraxial opioids: fentanyl

Sample item

Why does intrathecal fentanyl give rapid onset with a short duration compared with morphine?

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

The answer and the reasoning

B. High lipid solubility leads to quick spinal cord uptake and clearance

Lipophilic opioids enter the spinal cord and are cleared by the epidural vasculature rapidly, so analgesia appears within 5 to 10 minutes and lasts 2 to 4 hours, with minimal rostral spread.

Option by option

  • A. Rapid CSF metabolism

    CSF has little metabolic capacity.

  • B. High lipid solubility leads to quick spinal cord uptake and clearance (correct)

    Correct. Lipophilicity gives fast onset and short duration.

  • C. Lower affinity for mu receptors

    Fentanyl has high affinity for mu receptors.

  • D. Higher molecular weight

    Molecular weight is not the reason.

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 Anaesthesia question

What is the answer to this Anaesthesia question?

The best answer is B, High lipid solubility leads to quick spinal cord uptake and clearance. Lipophilic opioids enter the spinal cord and are cleared by the epidural vasculature rapidly, so analgesia appears within 5 to 10 minutes and lasts 2 to 4 hours, with minimal rostral spread.

Why is "Rapid CSF metabolism" not the answer?

CSF has little metabolic capacity.

Why is "Lower affinity for mu receptors" not the answer?

Fentanyl has high affinity for mu receptors.

Why is "Higher molecular weight" not the answer?

Molecular weight is not the reason.

What concept does this question test?

It tests Neuraxial opioids: fentanyl in Anaesthesia. The correct option holds because: Correct. Lipophilicity gives fast onset and short duration.

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 Neuraxial opioids: fentanyl?

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.