CNS drugs and antiepileptics: nalbuphine in opioid dependence: 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 · CNS drugs and antiepileptics: nalbuphine in opioid dependence

Sample item

A man who takes morphine daily for chronic pain receives nalbuphine after surgery. Within minutes he develops sweating, lacrimation, yawning and abdominal cramps. What is the most likely explanation?

ANalbuphine triggered serotonin syndromeBNalbuphine is a full mu agonist whose additive action caused cholinergic excessCNalbuphine is a kappa agonist with mu antagonist action and displaced morphine, precipitating withdrawalDNalbuphine inhibited morphine metabolism, causing toxicity

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

The answer and the reasoning

C. Nalbuphine is a kappa agonist with mu antagonist action and displaced morphine, precipitating withdrawal

Nalbuphine is a kappa agonist that blocks or only partly activates mu receptors. In a patient with physical dependence on a full mu agonist, it displaces the agonist and precipitates withdrawal. Pentazocine, butorphanol and buprenorphine behave in a similar way.

Option by option

A. Nalbuphine triggered serotonin syndrome
Serotonin syndrome features clonus and hyperthermia, which are not described.
B. Nalbuphine is a full mu agonist whose additive action caused cholinergic excess
A full mu agonist would add to the morphine effect and not produce withdrawal.
C. Nalbuphine is a kappa agonist with mu antagonist action and displaced morphine, precipitating withdrawal (correct)
Correct. Mu antagonist action displaced morphine and precipitated withdrawal.
D. Nalbuphine inhibited morphine metabolism, causing toxicity
Nalbuphine does not inhibit morphine metabolism, and morphine toxicity would cause miosis and sedation.

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.

Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is C, Nalbuphine is a kappa agonist with mu antagonist action and displaced morphine, precipitating withdrawal. Nalbuphine is a kappa agonist that blocks or only partly activates mu receptors.

Why is "Nalbuphine triggered serotonin syndrome" not the answer?

Serotonin syndrome features clonus and hyperthermia, which are not described.

Why is "Nalbuphine is a full mu agonist whose additive action caused choliner…" not the answer?

A full mu agonist would add to the morphine effect and not produce withdrawal.

Why is "Nalbuphine inhibited morphine metabolism, causing toxicity" not the answer?

Nalbuphine does not inhibit morphine metabolism, and morphine toxicity would cause miosis and sedation.

What concept does this question test?

It tests CNS drugs and antiepileptics: nalbuphine in opioid dependence in Pharmacology. In a patient with physical dependence on a full mu agonist, it displaces the agonist and precipitates withdrawal. Pentazocine, butorphanol and buprenorphine behave in a similar way.

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 CNS drugs and antiepileptics: nalbuphine in opioid dependence?

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.