My dad is having herpes virus infection in eye. he is taking valcivir medicn.please tell me for how long can a person take medicine without sideefect?

Depends: There is no hard set duration for side effects of valacyclovir. There are many people who tolerate it just fine for months/years because they need to take it to suppress herpes infection; that being said, it doesn't mean there aren't other people that will react to it. Each person's body is different.

Herpes: Herpes in the eye is not uncommon. We sometimes will ask patients to take a maintenance dose of Acyclovir or valcyclovir for a year (or years) to prevent recurrence. The initial treatment is usually 10-14 days depending on findings under the eye microscope.