CNS drugs and antiepileptics: mixed agonist-antagonist opioids: 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: mixed agonist-antagonist opioids

Sample item

A heroin-dependent man who is not currently in withdrawal receives an intravenous analgesic for renal colic. Within minutes he has yawning, sweating, abdominal cramps and dilated pupils. Which analgesic was most likely given?

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

The answer and the reasoning

B. Pentazocine

Pentazocine is a kappa agonist and a partial agonist or weak antagonist at the mu receptor. In a person physically dependent on a full mu agonist it displaces the opioid and precipitates withdrawal. Full mu agonists would instead add to the opioid effect.

Option by option

  • A. Methadone

    Methadone is a full mu agonist used to treat withdrawal.

  • B. Pentazocine (correct)

    Correct. A mixed agonist-antagonist displaces the full agonist and precipitates withdrawal.

  • C. Fentanyl

    Fentanyl is a full mu agonist and would not precipitate withdrawal.

  • D. Morphine

    Morphine is a full mu agonist and would suppress withdrawal.

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, Pentazocine. Pentazocine is a kappa agonist and a partial agonist or weak antagonist at the mu receptor.

Why is "Methadone" not the answer?

Methadone is a full mu agonist used to treat withdrawal.

Why is "Fentanyl" not the answer?

Fentanyl is a full mu agonist and would not precipitate withdrawal.

Why is "Morphine" not the answer?

Morphine is a full mu agonist and would suppress withdrawal.

What concept does this question test?

It tests CNS drugs and antiepileptics: mixed agonist-antagonist opioids in Pharmacology. In a person physically dependent on a full mu agonist it displaces the opioid and precipitates withdrawal. Full mu agonists would instead add to the opioid effect.

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: mixed agonist-antagonist opioids?

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.