Valacyclovir (Valaciclovir) is an orally active antiviral drug for herpes simplex, herpes zoster, and herpes B, inhibiting HSV-1 W with an IC50 of 2.9 μg/ml. Valacyclovir is a prodrug of Aciclovir [1] [2] [3] [4] [5].

Valacyclovir (Valaciclovir; VACV) is absorbed in a concentration-dependent and saturable manner, characterized by a Michaelis-Menten constant (Km) of 1.64 mM and a maximum velocity (Vmax) of 23.34 nmol/mg protein/5 min. Comparable Km values observed in hPEPT1/CHO cells, along with rat and rabbit tissues and Caco-2 cells, indicate that hPEPT1 primarily governs VACV's intestinal transport properties in vitro [5].

A comparative study demonstrated that Valacyclovir, administered at a dosage of 1 g twice daily, is equally effective as Acyclovir taken at 200 mg five times daily for a 10-day period in treating the initial outbreak of genital herpes. Similarly, for managing recurrent episodes, Valacyclovir proves just as effective as Acyclovir with a 5-day treatment course. Furthermore, a daily regimen of 1 g of Valacyclovir is found to be as efficacious as a 2 g daily dose, and it can be taken once daily [1]. In a pharmacokinetic assessment, the serum and CSF concentrations of Acyclovir reached steady state after six days of administering Valacyclovir at 1,000 mg three times daily [2]. In cellular studies, EC50 values for PE and AC indicated differing efficacies across 3T3 and BHK cells, highlighting the intricacies of drug action in various cell types. In immunosuppressed mice infected with the virus, treatment with FA and VA significantly reduced symptoms like erythema, ear paralysis, and lesions, and prevented death, eliminating the virus from the ear and brainstem within six days. However, the virus reemerged after treatment cessation in the VA group [3].