Opioids: morphine in renal failure: 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.

Try it

Pharmacology · Opioids: morphine in renal failure

Sample item

A 70-year-old man with end-stage kidney disease and cancer pain on oral morphine becomes drowsy with pinpoint pupils, myoclonic jerks and slow breathing. What explains his toxicity, and what is a better analgesic choice?

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

The answer and the reasoning

B. Accumulation of active morphine-6-glucuronide; switch to fentanyl

Morphine is conjugated to morphine-6-glucuronide, a potent active metabolite, and to inactive morphine-3-glucuronide, both of which are renally excreted. In renal failure they accumulate and cause sedation, respiratory depression and neuroexcitation. Fentanyl or methadone, metabolised mainly by the liver to inactive products, is safer, whereas codeine and pethidine also have problematic metabolites.

Option by option

  • A. Failure of conjugation by the liver; switch to pethidine

    Hepatic conjugation is intact in renal failure, and pethidine produces neurotoxic norpethidine.

  • B. Accumulation of active morphine-6-glucuronide; switch to fentanyl (correct)

    Accumulating active glucuronide explains the toxicity and fentanyl avoids it.

  • C. Accumulation of norpethidine; switch to codeine

    Norpethidine accumulation is a feature of pethidine, and codeine also yields active metabolites that accumulate in renal failure.

  • D. Enzyme induction by morphine; switch to a higher dose of tramadol

    Morphine is not an enzyme inducer, and tramadol at high dose adds seizure and serotonergic risk.

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 Pharmacology questions

Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is B, Accumulation of active morphine-6-glucuronide; switch to fentanyl. Morphine is conjugated to morphine-6-glucuronide, a potent active metabolite, and to inactive morphine-3-glucuronide, both of which are renally excreted.

Why is "Failure of conjugation by the liver; switch to pethidine" not the answer?

Hepatic conjugation is intact in renal failure, and pethidine produces neurotoxic norpethidine.

Why is "Accumulation of norpethidine; switch to codeine" not the answer?

Norpethidine accumulation is a feature of pethidine, and codeine also yields active metabolites that accumulate in renal failure.

Why is "Enzyme induction by morphine; switch to a higher dose of tramadol" not the answer?

Morphine is not an enzyme inducer, and tramadol at high dose adds seizure and serotonergic risk.

What concept does this question test?

It tests Opioids: morphine in renal failure in Pharmacology. In renal failure they accumulate and cause sedation, respiratory depression and neuroexcitation. Fentanyl or methadone, metabolised mainly by the liver to inactive products, is safer, whereas codeine and pethidine also have problematic metabolites.

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 Opioids: morphine in renal failure?

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.