Virology: ganciclovir-resistant cytomegalovirus: 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 · Virology: ganciclovir-resistant cytomegalovirus

Sample item

A kidney transplant recipient has cytomegalovirus viraemia that rises despite 3 weeks of adequately dosed intravenous ganciclovir. Genotyping shows a mutation in the UL97 gene. What is the most appropriate change in therapy?

AContinue the same ganciclovir for a longer courseBHigh-dose oral aciclovirCOral valganciclovir at the same doseDIntravenous foscarnet

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

The answer and the reasoning

D. Intravenous foscarnet

Ganciclovir must be monophosphorylated by the viral UL97 kinase before host kinases complete activation, and UL97 mutations are the commonest cause of resistance. Foscarnet binds the pyrophosphate site of the DNA polymerase directly and needs no viral kinase activation, so it remains active. Its main toxicity is nephrotoxicity and electrolyte disturbance.

Option by option

A. Continue the same ganciclovir for a longer course
Longer ganciclovir cannot overcome a phosphorylation defect.
B. High-dose oral aciclovir
Aciclovir needs a thymidine kinase that cytomegalovirus lacks, so it is a poor option.
C. Oral valganciclovir at the same dose
Valganciclovir is a prodrug of ganciclovir and shares the same activation step.
D. Intravenous foscarnet (correct)
Foscarnet acts directly on viral DNA polymerase and bypasses the defective kinase step.

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.

Questions about this Microbiology question

What is the answer to this Microbiology question?

The best answer is D, Intravenous foscarnet. Ganciclovir must be monophosphorylated by the viral UL97 kinase before host kinases complete activation, and UL97 mutations are the commonest cause of resistance.

Why is "Continue the same ganciclovir for a longer course" not the answer?

Longer ganciclovir cannot overcome a phosphorylation defect.

Why is "High-dose oral aciclovir" not the answer?

Aciclovir needs a thymidine kinase that cytomegalovirus lacks, so it is a poor option.

Why is "Oral valganciclovir at the same dose" not the answer?

Valganciclovir is a prodrug of ganciclovir and shares the same activation step.

What concept does this question test?

It tests Virology: ganciclovir-resistant cytomegalovirus in Microbiology. Foscarnet binds the pyrophosphate site of the DNA polymerase directly and needs no viral kinase activation, so it remains active. Its main toxicity is nephrotoxicity and electrolyte disturbance.

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 Virology: ganciclovir-resistant cytomegalovirus?

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.