CNS drugs and antiepileptics: barbiturate induction and porphyria: 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: barbiturate induction and porphyria

Sample item

A 30-year-old woman has recurrent colicky abdominal pain, psychiatric disturbance and urine that darkens on standing. She needs emergency surgery under general anaesthesia. Which induction agent should be avoided because it can precipitate an acute attack?

APropofolBThiopentoneCNitrous oxideDFentanyl

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

The answer and the reasoning

B. Thiopentone

In acute hepatic porphyrias, drugs that induce hepatic delta-aminolevulinic acid synthase can provoke an attack. Barbiturates such as thiopentone are strong inducers and are contraindicated. Propofol, opioids and nitrous oxide are regarded as safe.

Option by option

A. Propofol
Propofol is considered safe in acute porphyria and is commonly chosen for induction.
B. Thiopentone (correct)
Correct. Barbiturates induce ALA synthase and can precipitate acute porphyric attacks.
C. Nitrous oxide
Nitrous oxide is considered safe in porphyria and is not an enzyme inducer.
D. Fentanyl
Fentanyl is considered safe in porphyria and does not induce ALA synthase.

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 B, Thiopentone. In acute hepatic porphyrias, drugs that induce hepatic delta-aminolevulinic acid synthase can provoke an attack.

Why is "Propofol" not the answer?

Propofol is considered safe in acute porphyria and is commonly chosen for induction.

Why is "Nitrous oxide" not the answer?

Nitrous oxide is considered safe in porphyria and is not an enzyme inducer.

Why is "Fentanyl" not the answer?

Fentanyl is considered safe in porphyria and does not induce ALA synthase.

What concept does this question test?

It tests CNS drugs and antiepileptics: barbiturate induction and porphyria in Pharmacology. Barbiturates such as thiopentone are strong inducers and are contraindicated. Propofol, opioids and nitrous oxide are regarded as safe.

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 CNS drugs and antiepileptics: barbiturate induction and porphyria?

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.