Viral infections: acyclovir-resistant herpes: practice question

A Dermatology 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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Dermatology · Viral infections: acyclovir-resistant herpes

Sample item

An HIV positive patient has persistent perianal herpetic ulcers despite adequate oral acyclovir, and the virus is thymidine kinase deficient. Which drug is appropriate?

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

The answer and the reasoning

A. Intravenous foscarnet

Acyclovir, valacyclovir and famciclovir all need viral thymidine kinase for activation. Foscarnet directly inhibits viral DNA polymerase and does not need activation, so it works in thymidine kinase deficient strains.

Option by option

  • A. Intravenous foscarnet (correct)

    Correct. Foscarnet bypasses the need for thymidine kinase.

  • B. Oral valacyclovir

    Valacyclovir is a prodrug of acyclovir and shares the same resistance.

  • C. Intravenous ganciclovir

    Ganciclovir is also phosphorylated by thymidine kinase in HSV.

  • D. Oral famciclovir

    Famciclovir also depends on viral thymidine kinase.

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 Dermatology question

What is the answer to this Dermatology question?

The best answer is A, Intravenous foscarnet. Acyclovir, valacyclovir and famciclovir all need viral thymidine kinase for activation.

Why is "Oral valacyclovir" not the answer?

Valacyclovir is a prodrug of acyclovir and shares the same resistance.

Why is "Intravenous ganciclovir" not the answer?

Ganciclovir is also phosphorylated by thymidine kinase in HSV.

Why is "Oral famciclovir" not the answer?

Famciclovir also depends on viral thymidine kinase.

What concept does this question test?

It tests Viral infections: acyclovir-resistant herpes in Dermatology. Foscarnet directly inhibits viral DNA polymerase and does not need activation, so it works in thymidine kinase deficient strains.

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 Viral infections: acyclovir-resistant herpes?

Learn each condition by its primary lesion, site and signature sign. Then use the flashcards and the other Dermatology 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.