Valacyclovir (Valaciclovir) is an orally active antiviral drug for herpes simplex, herpes zoster, and herpes B. Valacyclovir inhibits 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) uptake was concentration dependent and saturable with a Michaelis-Menten constant and maximum velocity of 1.64 mM and 23.34 nmol/mg protein/5 min, respectively. A very similar Km value was obtained in hPEPT1/CHO cells and in rat and rabbit tissues and Caco-2 cells, which demonstrates that hPEPT1 dominates the intestinal transport properties of VACV in vitro [5].

A large comparative trial has shown that Valacyclovir (1 g twice a day) is as same effective as acyclovir (200 mg five times a day) when given for 10 days for treatment of the first episode of genital herpes. For treating recurrences, two trials show that valacyclovir is as effective as acyclovir (200 mg five times a day) with a treatment period of 5 days. A daily dose of 1 g of valacyclovir is as effective as 2 g daily. Valacyclovir can be administered once a day [1]. The concentrations of acyclovir in serum and CSF were measured at steady state after 6 days of oral treatment with 1,000 mg of valacyclovir three times a day [2]. EC50 values of PE and AC in 3T3 cells were 0.02 and 0.01 ug/ml, while values in BHK cells were 0.2 and 0.03 ug/ml. Treatment of infected immunosuppressed mice and FA and VA (b.i.d., 5.5 days) reduced the proportion with erythema from 100% to 24% and 38%, and eliminated ear paralysis, ear lesions (vesicles, etc) and death. Virus was absent from ear and brainstem by day 6, but reappeared after discontinuation in mice treated with VA [3].