Mycology: antifungal mechanisms, terbinafine: practice question

A Microbiology 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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Microbiology · Mycology: antifungal mechanisms, terbinafine

Sample item

A diabetic man has Trichophyton rubrum toenail onychomycosis and is started on oral terbinafine. Which enzyme does this drug inhibit?

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

The answer and the reasoning

A. Squalene epoxidase

Terbinafine, an allylamine, inhibits squalene epoxidase and so blocks ergosterol synthesis early. Ergosterol deficiency and toxic intracellular squalene accumulation make it fungicidal against dermatophytes. It concentrates in nails and skin and is the preferred oral agent for onychomycosis.

Option by option

  • A. Squalene epoxidase (correct)

    Correct. Squalene epoxidase inhibition is the action of terbinafine.

  • B. Fungal beta-tubulin polymerisation

    Disruption of microtubules and mitosis is the mechanism of griseofulvin.

  • C. Lanosterol 14-alpha demethylase

    Lanosterol 14-alpha demethylase is the target of azoles such as itraconazole and fluconazole.

  • D. 1,3-beta-D-glucan synthase

    1,3-beta-D-glucan synthase is the target of echinocandins.

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 Microbiology questions

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is A, Squalene epoxidase. Terbinafine, an allylamine, inhibits squalene epoxidase and so blocks ergosterol synthesis early.

Why is "Fungal beta-tubulin polymerisation" not the answer?

Disruption of microtubules and mitosis is the mechanism of griseofulvin.

Why is "Lanosterol 14-alpha demethylase" not the answer?

Lanosterol 14-alpha demethylase is the target of azoles such as itraconazole and fluconazole.

Why is "1,3-beta-D-glucan synthase" not the answer?

1,3-beta-D-glucan synthase is the target of echinocandins.

What concept does this question test?

It tests Mycology: antifungal mechanisms, terbinafine in Microbiology. Ergosterol deficiency and toxic intracellular squalene accumulation make it fungicidal against dermatophytes. It concentrates in nails and skin and is the preferred oral agent for onychomycosis.

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 Mycology: antifungal mechanisms, terbinafine?

Make a one-line identity card for each organism: shape and stain, defining test, toxin, disease and drug. Then use the flashcards and the other Microbiology 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.