Autonomic: physostigmine versus neostigmine: 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: physostigmine versus neostigmine

Sample item

Why can physostigmine reverse the central features of anticholinergic poisoning whereas neostigmine cannot?

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

The answer and the reasoning

B. Physostigmine is a tertiary amine that crosses the blood-brain barrier

Physostigmine is a lipid-soluble tertiary amine reaching the CNS, whereas neostigmine is a quaternary ammonium compound with poor central penetration. This explains why physostigmine is used for central anticholinergic delirium.

Option by option

  • A. Physostigmine is irreversible in action

    Physostigmine is a reversible carbamate inhibitor.

  • B. Physostigmine is a tertiary amine that crosses the blood-brain barrier (correct)

    Correct. Central penetration depends on the tertiary amine structure.

  • C. Neostigmine acts only on nicotinic receptors

    Neostigmine increases acetylcholine at muscarinic and nicotinic sites.

  • D. Physostigmine is a direct muscarinic agonist

    Physostigmine inhibits cholinesterase and is not a direct agonist.

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.

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Questions about this Pharmacology question

What is the answer to this Pharmacology question?

The best answer is B, Physostigmine is a tertiary amine that crosses the blood-brain barrier. Physostigmine is a lipid-soluble tertiary amine reaching the CNS, whereas neostigmine is a quaternary ammonium compound with poor central penetration.

Why is "Physostigmine is irreversible in action" not the answer?

Physostigmine is a reversible carbamate inhibitor.

Why is "Neostigmine acts only on nicotinic receptors" not the answer?

Neostigmine increases acetylcholine at muscarinic and nicotinic sites.

Why is "Physostigmine is a direct muscarinic agonist" not the answer?

Physostigmine inhibits cholinesterase and is not a direct agonist.

What concept does this question test?

It tests Autonomic: physostigmine versus neostigmine in Pharmacology. This explains why physostigmine is used for central anticholinergic delirium.

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 Autonomic: physostigmine versus neostigmine?

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.