An AIDS patient with CMV retinitis who progressed despite adequate ganciclovir therapy is found to have an UL97 kinase mutation conferring ganciclovir resistance. The most appropriate alternative agent is:

• A Acyclovir
• B Famciclovir
• C Ribavirin
• D Foscarnet ✓

Explanation

Ganciclovir requires phosphorylation by the viral UL97 kinase to its active triphosphate form, so mutations in UL97 confer resistance. Foscarnet is a pyrophosphate analog that directly inhibits viral DNA polymerase at the pyrophosphate binding site without needing any viral kinase for activation, making it effective against ganciclovir-resistant CMV. Acyclovir and famciclovir have inadequate CMV activity, and ribavirin is used for RSV and hepatitis D, not CMV retinitis. Foscarnet itself is nephrotoxic and causes electrolyte wasting.

Reference: Katzung Basic and Clinical Pharmacology, 15th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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