A patient with CMV retinitis develops leucopenia that forces withdrawal of ganciclovir. Viral load confirms ganciclovir resistant CMV due to UL97 kinase mutations. Which drug acts independently of viral kinase phosphorylation and is appropriate here?

• A Valganciclovir
• B Cidofovir
• C Acyclovir
• D Foscarnet ✓

Explanation

Foscarnet directly inhibits viral DNA polymerase by binding the pyrophosphate binding site and needs no activation by viral or cellular kinases, so UL97 mutant CMV remains susceptible. Its major toxicities are nephrotoxicity and electrolyte wasting of calcium, magnesium, potassium and phosphate, requiring saline loading and monitoring. Valganciclovir shares cross resistance with ganciclovir through the same pathway, and cidofovir still needs cellular kinases though not UL97.

Reference: Harrison's Principles of Internal Medicine, 21st ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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