Autonomic nervous system: methylnaltrexone: 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 · Autonomic nervous system: methylnaltrexone

Sample item

A palliative care patient on long-term oral morphine has severe constipation despite senna and lactulose. Pain control must not be reversed. Which agent is suitable?

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

The answer and the reasoning

D. Methylnaltrexone

Methylnaltrexone is a quaternary derivative of naltrexone, so it does not cross the blood-brain barrier. It blocks mu receptors in the gut and relieves opioid-induced constipation without reversing central analgesia. Naloxone and naltrexone act centrally and can precipitate withdrawal or pain.

Option by option

  • A. Naltrexone orally

    Naltrexone has central effects and can reverse analgesia and precipitate withdrawal.

  • B. Loperamide

    Loperamide is a gut opioid agonist and would worsen constipation.

  • C. Naloxone intravenously

    Intravenous naloxone crosses into the brain and reverses analgesia.

  • D. Methylnaltrexone (correct)

    Correct. A peripherally restricted mu antagonist relieves constipation and leaves analgesia intact.

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 D, Methylnaltrexone. Methylnaltrexone is a quaternary derivative of naltrexone, so it does not cross the blood-brain barrier.

Why is "Naltrexone orally" not the answer?

Naltrexone has central effects and can reverse analgesia and precipitate withdrawal.

Why is "Loperamide" not the answer?

Loperamide is a gut opioid agonist and would worsen constipation.

Why is "Naloxone intravenously" not the answer?

Intravenous naloxone crosses into the brain and reverses analgesia.

What concept does this question test?

It tests Autonomic nervous system: methylnaltrexone in Pharmacology. It blocks mu receptors in the gut and relieves opioid-induced constipation without reversing central analgesia. Naloxone and naltrexone act centrally and can precipitate withdrawal or pain.

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 Autonomic nervous system: methylnaltrexone?

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.