Ganciclovir is more effective than acyclovir against
**Core Concept**
Ganciclovir and acyclovir are both antiviral medications used to treat cytomegalovirus (CMV) infections. The primary difference between these two drugs lies in their mechanism of action and resistance patterns. Specifically, ganciclovir is more effective than acyclovir due to its ability to penetrate cells more efficiently and its higher affinity for the CMV DNA polymerase enzyme.
**Why the Correct Answer is Right**
Ganciclovir is a nucleoside analog that is metabolized to its active form, ganciclovir triphosphate, which then inhibits the CMV DNA polymerase enzyme. This inhibition prevents the replication of viral DNA, effectively treating CMV infections. Unlike acyclovir, ganciclovir does not require activation by viral thymidine kinase (TK), making it more effective against CMV-infected cells.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because ganciclovir's mechanism of action is not dependent on viral thymidine kinase (TK), unlike acyclovir.
**Option B:** This option is incorrect because ganciclovir's higher affinity for the CMV DNA polymerase enzyme is not a characteristic of acyclovir.
**Option C:** This option is incorrect because ganciclovir's ability to penetrate cells more efficiently is not a property of acyclovir.
**Option D:** This option is incorrect because ganciclovir's efficacy against CMV infections is not due to its ability to inhibit viral protein synthesis.
**Clinical Pearl / High-Yield Fact**
Ganciclovir is often used in combination with foscarnet to treat CMV retinitis, particularly in immunocompromised patients. This combination therapy has been shown to improve outcomes and reduce the risk of resistance.
**Correct Answer:** C. CMV-infected cells