- Guanosine nucleoside analogue similar to acyclovir
- Inhibits all human herpesviruses by inhibiting DNA polymerase
- Resistance in CMV
- Most often conferred by mutations of UL97 kinase, which is required in order to phosphorylate ganciclovir into its active form
- Can also develop through mutations in the target UL54 DNA polymerase
- Oral bioavailability 6-8%
