Designed on the basis of acyclovir, vasiclovir is broken down to acyclovir in the body and has a higher oral bioavailability than acyclovir. Vasiclovir is the L-valine ester of acyclovir, which is almost entirely and rapidly broken down in the body by the enzyme vasiclovir hydrolase to acyclovir and valine, thus exerting antiviral effects. The bioavailability of acyclovir in 1000 mg of vasiclovir is 54% and is not affected by food. Compared to oral acyclovir, the area under the drug-time curve after vasiclovir administration was 2 to 3 times higher and bioavailability was significantly increased. Acyclovir and valaciclovir are both commonly used antiviral drugs in clinical practice and may differ in clinical efficacy, so they should be used under the guidance of a physician to avoid adverse effects.