CNS drugs and antiepileptics: ester local anaesthetic allergy: 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: ester local anaesthetic allergy

Sample item

A patient reports a rash and swelling after dental procaine in the past. A different local anaesthetic is needed for a minor procedure. Which is the safest choice?

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

The answer and the reasoning

A. Lignocaine

Procaine is an ester local anaesthetic metabolised to para-aminobenzoic acid, which is the usual allergen. Amide agents such as lignocaine are not metabolised to PABA and rarely cause cross-sensitivity.

Option by option

  • A. Lignocaine (correct)

    Correct. Lignocaine is an amide and is not broken down to PABA.

  • B. Tetracaine

    Tetracaine is an ester that also yields PABA, so cross-reactivity is expected.

  • C. Chloroprocaine

    Chloroprocaine is an ester and is metabolised to a PABA derivative.

  • D. Benzocaine

    Benzocaine is an ester related to PABA and is a frequent sensitiser.

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 A, Lignocaine. Procaine is an ester local anaesthetic metabolised to para-aminobenzoic acid, which is the usual allergen.

Why is "Tetracaine" not the answer?

Tetracaine is an ester that also yields PABA, so cross-reactivity is expected.

Why is "Chloroprocaine" not the answer?

Chloroprocaine is an ester and is metabolised to a PABA derivative.

Why is "Benzocaine" not the answer?

Benzocaine is an ester related to PABA and is a frequent sensitiser.

What concept does this question test?

It tests CNS drugs and antiepileptics: ester local anaesthetic allergy in Pharmacology. Amide agents such as lignocaine are not metabolised to PABA and rarely cause cross-sensitivity.

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: ester local anaesthetic allergy?

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.