What is the mechanism of action for Valacyclovir?

Valacyclovir is an antiviral medication predominantly used to treat infections caused by certain viruses, such as herpes simplex virus and varicella-zoster virus. Its mechanism of action involves the inhibition of viral DNA synthesis through a process known as chain termination.

When Valacyclovir is administered, it is converted into acyclovir in the body. Acyclovir is then phosphorylated by viral enzymes, leading to the formation of acyclovir triphosphate. This active form of the drug competes with deoxyguanosine triphosphate for incorporation into the growing viral DNA strand. When it is incorporated into the DNA, it causes chain termination because it lacks a crucial 3'-OH group required for further elongation of the DNA, effectively halting viral replication.

This targeted mechanism makes Valacyclovir effective in managing viral infections, distinguishing it from antibiotics, which inhibit bacterial processes or disrupt cell walls. Likewise, antifungal action does not apply to Valacyclovir, as its activity is specific to viral pathogens, not fungal ones, and it does not directly inhibit protein synthesis in viruses. Therefore, the correct choice reflects how Valacyclovir effectively disrupts viral replication by terminating DNA strand synthesis.