Buy Valcivir 500mg contain valacyclovir, a prodrug of acyclovir that is more readily absorbed and is converted to acyclovir by the liver. Valacyclovir in Valcivir tablets 500mg then works in the same way as acyclovir, as an antiviral agent that is highly active against both types of herpes simplex virus, HSV-I, that causes cold sores and HSV-II that causes genital herpes; and also against the closely related varicella zoster herpes virus that causes chicken pox and shingles.