Valaciclovir, or its active form aciclovir, is a so-called antimetabolite for the DNA of the herpes virus. It is incorporated into the DNA of the virus due to its structural similarity to the nucleic base guanine. This causes the DNA strand to break and the virus cannot replicate further. It has no effect on the DNA of healthy cells.
The oral bioavailability of valaciclovir is approximately 54% and protein binding is 13-17%. Degradation is not catalyzed by enzymes of the CYP450 system, but by various other enzymes (dehydrogenases and oxidases). Over 90% of the ingested dose is excreted in the urine. The elimination half-life is about 2-3 hours.