Antiviral drugs: 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 · Antiviral drugs

Sample item

Why is acyclovir selectively toxic to herpes-infected cells?

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

The answer and the reasoning

B. It is first phosphorylated by viral thymidine kinase

Acyclovir is a guanosine analogue converted to its monophosphate only by herpesvirus thymidine kinase, then to the triphosphate by host kinases. The triphosphate inhibits viral DNA polymerase and terminates the chain, so uninfected cells are largely spared.

Option by option

  • A. It inhibits reverse transcriptase

    Reverse transcriptase inhibition is the action of anti-HIV nucleoside analogues.

  • B. It is first phosphorylated by viral thymidine kinase (correct)

    Initial activation depends on the viral enzyme, concentrating the drug in infected cells.

  • C. It inhibits viral neuraminidase

    Neuraminidase inhibition is how oseltamivir acts on influenza.

  • D. It blocks the M2 ion channel and uncoating

    M2 channel blockade and uncoating inhibition is the action of amantadine.

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, It is first phosphorylated by viral thymidine kinase. Acyclovir is a guanosine analogue converted to its monophosphate only by herpesvirus thymidine kinase, then to the triphosphate by host kinases.

Why is "It inhibits reverse transcriptase" not the answer?

Reverse transcriptase inhibition is the action of anti-HIV nucleoside analogues.

Why is "It inhibits viral neuraminidase" not the answer?

Neuraminidase inhibition is how oseltamivir acts on influenza.

Why is "It blocks the M2 ion channel and uncoating" not the answer?

M2 channel blockade and uncoating inhibition is the action of amantadine.

What concept does this question test?

It tests Antiviral drugs in Pharmacology. The triphosphate inhibits viral DNA polymerase and terminates the chain, so uninfected cells are largely spared.

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 Antiviral drugs?

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.