Page 246 - First Aid for the USMLE Step 1 2020, Thirtieth edition [MedicalBooksVN.com]_Neat

202 SEcTioN ii Microbiology ` microbiology—aNtimicrobials Microbiology ` microbiology—aNtimicrobials

Ganciclovir
mecHaNism 5′-monophosphate formed by a CMV viral kinase. Guanosine analog. Triphosphate formed by
cellular kinases. Preferentially inhibits viral DNA polymerase.

cliNical Use CMV, especially in immunocompromised patients. Valganciclovir, a prodrug of ganciclovir, has
better oral bioavailability.
aDVerse eFFects Bone marrow suppression (leukopenia, neutropenia, thrombocytopenia), renal toxicity. More toxic
to host enzymes than acyclovir.
mecHaNism oF resistaNce Mutated viral kinase.

Foscarnet
mecHaNism Viral DNA/RNA polymerase inhibitor and Foscarnet = pyrofosphate analog.
HIV reverse transcriptase inhibitor. Binds to
pyrophosphate-binding site of enzyme. Does
not require any kinase activation.
cliNical Use CMV retinitis in immunocompromised patients
when ganciclovir fails; acyclovir-resistant HSV.

aDVerse eFFects Nephrotoxicity, electrolyte abnormalities
(hypo- or hypercalcemia, hypo- or
hyperphosphatemia, hypokalemia,
hypomagnesemia) can lead to seizures.

mecHaNism oF resistaNce Mutated DNA polymerase.

Cidofovir

mecHaNism Preferentially inhibits viral DNA polymerase. Does not require phosphorylation by viral kinase.
cliNical Use CMV retinitis in immunocompromised patients; acyclovir-resistant HSV. Long half-life.
aDVerse eFFects Nephrotoxicity (coadminister with probenecid and IV saline to  toxicity).

FAS1_2019_03-Microbiology.indd 202 11/14/19 12:22 PM